Invariably, few can deny the integral roles of conscious free will and volition in our identities, beliefs, choices, interactions, and everyday lives.

Introduction:

Let’s get started with the main course. Would you prefer course A, a fried chicken burger, or course B, stuffed buffalo wings? Whichever was chosen, most would feel certain that they made the decision themselves. After all, the decision was made exclusively by yourself and hopefully without outside influence. Simply, your freedom to choose would be considered free will as you are in control of your decisions.

But let’s repeat the question again. Say we rewind time and allowed you to pick between the courses, would you consistently choose one over the other? Or would it be randomized? The difference, though minuscule, is key in differentiating between physical determinism and free will.

Within society, the great debate between physical determinism and free will resides as an impending topic within a broader paradigm of Nature vs. Nurture. Physical determinism outlines the Nature aspect of our biological functions having priority control over our actions and rationale, while free will outlines the Nurture aspect of a person’s freedom in paving their own path independently from their biology. In terms of the US population, a sample study was conducted by David Wisniewski, Robert Deutschlände, and John-Dylan Haynes, where they used a Free Will Inventory (FWI) assessment to gauge the beliefs between free will and determinism of 900 individuals residing within the US [1]. The study found that 82.33% of individuals believed in Free Will, 30.77% believed in determinism, and 75% of individuals believed in a mixture of both. Though the majority of sampled individuals are aligned with believing in free will, in context to the 75% of individuals believing in both, we must keep an open mind when exploring the topic of free will and understand the spectrum is neither fully black nor white nor a perfect mix of gray [1]. Within our article, we will discuss the neurobiological research conducted by various researchers to explore free will within the scope of neuroscience and understand the development of how neuroscience began playing a larger role in revealing hidden components. For focus, our article will discuss a neurological indicator of free will within voluntary muscle movements, readiness potential. 

Discovery of readiness potential:

On a typical day in Spring 1964, chief physician of neurology Hans Kornhuber and his doctoral student Lüder Deecke went for their usual lunch at the base of the Schlossberg hill in Freiburg, Germany [2]. While dining alone in the vibrant garden, the two discussed their annoyance with the current direction of brain research, as both believed that neuroscience should be focused more on exploring the processing of self-initiated actions and free will in the brain. Following this inspiration, the two scientists decided to take on the task of studying free will and volition themselves by looking for brain potentials associated with intentional and voluntary movements. By taking voluntary movement as their research paradigm, the two serendipitously stumbled upon a cerebral potential, then called Bereitschaftspotential, that would revolutionize neuroscience research for decades to come [2]. 

The Bereitschaftspotential, also colloquially known as the readiness potential, is essentially the duration that it took for an electrical impulse (signal) to arrive to a motor neuron after a person’s intent to move [2]. After over 100 specific movements recorded by an electroencephalogram (EEG) from 12 subjects, Kornhuber and Deeke  were able to average the electrical potential difference to be around 10-15 microvolts with the duration being less than 30-90 milliseconds. This 10-15 microvolts change in electrical potential indicated activity and communication between neurons before a voluntary movement [2]. 

Undoubtedly, the discovery of the readiness potential in 1964 was ground-breaking in defining the junction between the boundaries of intention and execution within motor neurons. From measuring 100 movements of 12 subjects in 94 experiments using an electroencephalogram (EEG), the two researchers were able to study the duration and amplitude of readiness potential [2]. The readiness potential, measured from a voluntary movement, averaged around 10-15 microvolts, indicating a slow increase in negative electrical activity in the surface layer of the cortex, which occurs for less than 30-90 milliseconds. Thus, Kornhuber and Deecke coined the term bereitschaftspotential to describe a change in electrical activity in the brain that occurs just before a voluntary movement is made, signaling that the brain is getting ready to perform an action [2].

The discovery of the readiness potential was so paramount because it uncovered evidence of a neural mechanism underlying voluntary decisions and movement. This discovery of slow, gradual electrical change that reliably appears in the brain before a person executes a voluntary action challenged the previous belief that the conscious will alone entirely controlled voluntary movements. Instead, Kornhuber and Deecke’s discovery suggested a process of unconscious neural preparation before conscious decision-making. At the same time, the discovery of readiness potential also produced questions such as whether or not we can actually decide to perform an action, or if the readiness potential occurs before or after we think to make that movement. Like Pandora's Box, this research opened the door for further investigation into the neural basis of movement and consciousness in decades to come, provoking the question of  whether free will even exists.

Exploring the role of readiness potential in voluntary movement

It is impossible to begin discussing the neuroscientific foundation of free will without first examining the pioneering work of Benjamin Libet. In the 1970s, Benjamin Libet was a neuroscience researcher in the physiology department of the University of California, San Francisco, particularly interested in neural activity and sensation threshold research. His initial experiments in the field focused primarily on finding how many activations of different brain regions were necessary to trigger artificial bodily sensations. This work soon evolved into a probe of human consciousness and the unconscious brain activity underlying conscious will and decision. Extending Kornhuber and Deecke’s research, Libet explored how the occurrence of readiness potential before a physical action relates to the voluntary intention to move. For the purposes of the study, Libet defined readiness potential as electrophysiological signals that show when the brain is prepared to act half a second before a spontaneous voluntary act [3]. By using an electromyogram (EMG), a technique that determines muscle response or electrical activity following a nerve's stimulation of the muscle, Libet measured the onset of readiness potential generated before each voluntary event, when participants became first aware of the decision to perform an action [3]. This was done by measuring when participants became consciously aware of their decision to move a finger while observing a rapidly moving dot designed to mimic a clock hand movement. During the experiment, the participants observed the second hand of the clock and later recalled its position when they first felt a conscious awareness of their decision to move their finger [3]. 

Ultimately, the study found that the onset of readiness potential preceded the conscious decision to perform an action by an average of 0.35 seconds [3]. Libet interpreted the early onset of readiness potential and unconscious cerebral activity to be neuronal computation that unconsciously prepares a person to act. Based on these results, Libet suggested that people attribute willful control and awareness of their actions only because of their retroactive perspective of the act. Moreover, Libet and colleagues suggest that perhaps we have much less free will and volition control over our decisions and actions. Fundamentally, the Libet study presented a view on conscious will and resulting voluntary motor acts as being dictated by prior unconscious cerebral activity, challenging previous beliefs that our decisions and actions are entirely volitionally controlled at the conscious level of human mind [3].

Nevertheless, Libet’s paramount study also drew heavy criticism due to several key limitations [4]. Foremost, it is possible that there is a delay between a person's desire to act and their record of it, as this requires the subject to shift their focus from the volition to the action. Moreover, a person’s awareness and recollection of their decisions is often unreliable and subjective, hindering the ability of the subjects to accurately note the time they decided to move. A bigger issue with Libet’s findings is the lack of consensus and evidence that readiness potential even relates to the decisions to move or the action itself. Even if the actions are prepared and initiated on unconscious and preconscious levels, it is entirely possible that we make our decisions not only on a conscious level but also on a more intuitive, ambiguous, and impulsive level. Thus, Libet’s interpretation of free will could be problematic if volition and awareness of acting is strictly limited to conscious mind when it is entirely possible that free will and decision to act also extend to unconscious and subconscious mind. 

In a following 1985 paper, Libet extended his research on human consciousness by exploring the veto mechanism of conscious will in voluntary actions [5]. For the purposes of the study, Libet describes readiness potential as electrophysiological signals that show when the brain is prepared to act, starting roughly 0.55 seconds before a spontaneous voluntary act. According to the participants' memories, the conscious urge to act occurred approximately 0.2 seconds before the actual movement. Moreover, Libet's earlier discovery suggested that a person can "veto" a voluntary act during the 0.1 - 0.2 second  window before the action is carried out. Thus, Libet argues that the existence of "veto" control indicates that conscious will may influence the result of voluntary movement. Libet further proposes that while the initiation of a voluntary act begins unconsciously, conscious processes may play a substantial role in selecting and controlling the outcome of voluntary action. This way, conscious will can serve a permissive role, either permitting or preventing the motor execution following the unconscious intention to act [5]. Further research is required to objectively and holistically examine the role of brain activity in controlling and performing a voluntary movement.

Libet's research can also be used to support the concept that addiction is a brain disorder instead of a lack of willpower or control [6]. Namely, Libet's study supports the argument that uncontrolled unconscious processes drive addictive behaviors in the brain rather than conscious, willful decisions. This means that a person may not have full control over their addictive behavior, as it may be caused by unconscious processes related to the reward and reinforcement effects of the behavior on the brain. Such a perspective on addiction shifts the blame from the individual's choice in behavior to recognizing the role of unconscious brain processes in addiction [6]. Overall, application of Libet’s research on consciousness and free will highlights the need to reconsider clinical and behavioral treatment and support approaches to treat addiction. 

While many studies have shown that unconscious neural activity, like the readiness potential, precedes voluntary movement, scientists still do not agree on whether it is possible for a person to consciously control the action itself following this unconscious neural activity. Thus, a crucial question scientists have wondered about is the extent to which humans can consciously modify or control the movement initiated by the unconscious cerebral activity and what time frame is allotted to exert this conscious control. 

More recent studies, such as the one by German and Belgian researchers Soon, Brass, Heinze, and Haynes, further pursued the elusive role of unconscious processes in shaping voluntary decisions [7]. These researchers used functional magnetic resonance imaging (fMRI) to detect changes in blood oxygen levels of active and inactive brain areas and recorded brain activity as participants made decisions during a task. Higher blood oxygen levels in a brain region would indicate that the brain region is more active during a task. Subsequently, the study found that the outcome of a decision is reflected by increases in blood oxygen levels and neuron activity of the prefrontal and parietal cortices up to 10 seconds before it enters awareness. The fMRI data also indicated that the brain structures responsible for controlling voluntary movements and planning, initiation, and execution of movements encoded the outcome of the subject's decision during the execution phase. The study found that changes in blood oxygen levels and neuronal activity were detectable 4-7 seconds before the subject's conscious decision. These findings challenge the idea of human free will by providing evidence that the brain begins encoding a conscious decision considerable time before it enters conscious human awareness [7]. 

Encoding of movement in the cerebral cortex 

Attempting to better understand how voluntary behavior is encoded and initiated by the neuron circuitry of the human cerebral cortex, researchers at Harvard University and the University of California, Los Angeles examined the threshold of  brain activity in the human supplementary motor area and medial frontal cortex [8]. The medial frontal cortex is a region of the frontal lobe located in the center of the brain. This structure captured the interest of researchers due to its role in adaptive decision making, emotional regulation, and attention, as well as the processing and integrating information from multiple brain regions. The study documented and reviewed the activity of 1019 neurons in the medial frontal lobe while twelve epileptic subjects engaged in self-initiated finger movement upon feeling the urge to move. Results indicated that neuron activity of the supplementary motor area (SMA) gradually increased over approximately 1.5 seconds before participants reported deciding to move. Using 256 SMA neurons, researchers had greater than 80% accuracy in predicting participants' upcoming decision to act 0.7 seconds before the person became aware of their decisions. Furthermore, they developed a model to accurately predict when participants would become conscious of their decision to move 0.152 seconds on average before the actual reported urge to act [8]. 

While it was known that medial frontal lobe is involved in working memory, attention, motivation, error detection, and decision, this study proposes that the preconscious activity in the medial frontal lobe both precedes conscious will and can be used to predict when a person will be conscious of their decision to act [8]. While these neuronal activities and changes in the medial frontal lobe are not yet clearly related to the onset of a conscious decision to act, they suggested that a small population of neurons in the SMA can be used to accurately predict the emergence of free will and consciousness several hundred milliseconds before a subjects' awareness of the intention to act. Therefore, a person's awareness of the will to act may only occur once the threshold of active medial frontal neurons is reached. These simple neuronal mechanisms suggest a possible neurobiological model for producing volitionally driven behaviors. These findings support the view that awareness and free will emerges due to sufficient activity in the medial frontal cortex preceding conscious awareness, rather than conscious choice to exercise free will. Nevertheless, it still remained unclear what elicited sufficient activity in the medial frontal cortex preceding conscious and willful action [8]. 

Thus, for many years, Libet’s pioneering work remained largely unchallenged until French researchers Schurger, Sitt, and Dehaene proposed an accumulator model to address the possibly erroneous interpretation of readiness potential and its role in consciousness [9]. Simply, the accumulator model proposes a build-up of activity in a network of brain regions, including the medial frontal cortex, that leads to movement initiation. While a few past studies hinted that readiness potential might not cause voluntary actions at all, no study has ever provided an alternative explanation for the role of readiness potential. Thus, Schurger and colleagues took an unorthodox approach to Libet’s paradox by turning to the accumulator model of spontaneous neural activity prior to self-initiated movement. This accumulation or build-up of brain activity is presumed to be the accumulation of evidence in favor of a particular action, balanced by the regulatory activity of excitatory and inhibitory neurons. Once the evidence threshold is reached, the brain initiates the appropriate movement. In contrast to previous Libet-type studies that have repeatedly characterized readiness potential as the final stage of planning and preparation for movement, Schruger and colleagues propose an alternative explanation, wherein readiness potential buildup and consequent self-initiated movements reflect a gradual accumulation of random fluctuations in brain activity. To test this mathematical model, an experiment involved 16 participants who performed many trials of classical Libet tasks that were randomly interrupted using a compulsory auditory cue to press a button. A visual stimulus was displayed in each trial and participants responded using buttons. The participants pressed the button to indicate the position of the dot when they first felt the urge to press the button, similar to the classic Libet task. However, in this study, they were randomly interrupted by an auditory stimulus [9]. 

The study found that for any decision to be made, our neurons have to accumulate sufficient favorable evidence towards an action from external cues, such as from sensory stimuli, to cross a certain threshold of neuron activity [9]. Libet’s pioneering experiment had failed to provide participants with any external clues, leading the participants to act spontaneously whenever they felt the urge [3]. Replication of classical Libet tasks indicated that voluntary will to move coincided with haphazard and random fluctuations of participant’s brain activity [9]. The participants were more likely to move when the fluctuation of neural activity in the motor system of the brain approached the threshold for action initiation. These results imply that the brain does not decide to initiate a movement before a person becomes aware of it, as Libet had argued. Instead, the readiness potential likely reflects the rising part of the noisy and random brain activity fluctuations. If there are enough external cues to base our decision on, these fluctuations would reach a threshold of neuron activity sufficient enough to initiate a movement, saving people from endless irresolution when facing a random task [9]. 

To further test the results, Schuger and colleagues conducted an additional study examining brain noise in a group of people that didn’t move at all versus a group where people moved [9]. Then, an artificial-intelligence classifier determined the time at which brain activity of the two groups diverged. If Libet’s explanations were correct, then the divergence in brain activity should occur at 0.5 seconds. However, the artificial intelligence algorithm was unable to distinguish the brain activity of the two groups until about 0.15 seconds before the movement, which is around the time people reported being aware of their will to move in Libet’s original study. These results supported the idea that human’s subjective experience lines up with the time we make a decision [9]. 

To add to the conversation of free will, German researchers Jo, Hinterberger, Wittmann, Borghardt, and Schmidt studied whether brain activity reflects readiness potential and movement preparation [10]. The researchers used a  Libet-type self-initiated movement and auditory stimulus tasks where the participants indicated the clock-hand position upon feeling the urge to move. The study recorded brain activity of participants using electroencephalogram (EEG) and eye movement using electrooculography (EOG). Upon examining the brain's electrical activity, the study found that spontaneous fluctuations electrical shifts from negative to positive potential in brain activity are responsible for readiness potential. Upon examining these electrical shits, there was no difference in readiness potential whether the participant moved or not [10].

This fluctuation in readiness potential is not likely related to movement preparation, but rather enabling the decision for a self-initiated action [10]. The negative potential shifts make the decision more likely to occur, and the researchers use these results to challenge the explanations proposed by earlier Libet-type research. Consequently, because the results showed that readiness potential is the result of spontaneous brain activity the study argues that readiness potential cannot be used to prove or disprove free will [10]. 

On the one hand, we have determinists who believe our actions are predetermined by nature. They may say that the correlation between brain activity and the perception of time between actions means that unconscious brain processes determine our movement  On the contrary, supporters of free will may argue that the correlation between brain activity and the perception of time provides evidence for the brain's role in conscious decision-making and agency, showing how humans make deliberate choices. Now, with evidence that readiness potential is not an indicator of free will and readiness potential does not cause volition to arise or for voluntary action to be initiated, the researchers proposed the intentional binding effect model to uncover the causal link of preconscious brain activity and conscious will [10]. The intentional binding effect is a temporal phenomenon of particular interest, wherein people perceive the time between an action and its consequence as shorter than it actually is. To study the relationship between the readiness potential (RP) and the phenomenon of intentional binding, participants performed a task where they pressed a button in response to a visual cue and then rated the time between the button press and the appearance of a reward. The results of the study showed that the RP was correlated with the perceived time between the button press and the reward, suggesting that the RP may be related to intentional binding. The authors of the article discuss the implications of this finding and our understanding of voluntary action and the role of intention in shaping our perception. These results showed that early neural activity affects the perceived time of sensory outcomes from intentional actions The findings show a correlation between early readiness potential and temporal attraction that is suggested to be  caused by intentional action. These results shed light on the incomplete understanding of human volition and agency, indicating that neural representation of conscious intention to act, reflected by ongoing negative potential of the brain activity, may be associated with an enhanced sense of agency by predicting possible consequences of action [10].

Modification range

While pieces to the puzzle of conscious will were slowly put together, scientists from Berlin, Germany were especially interested in using brain-computer interface to pinpoint the time frame during which people can consciously modify or even cancel unconsciously initiated movements [11]. Using brain-computer interface (BCI) to predict and stop self-initiated motions before they occurred, the experiment employed 12 people, who sat in chairs facing a monitor with their right foot above a floor-mounted switch pedal. The use of a BCI device allowed for a direct communication between the brain and a computer, bypassing the need for muscle movement to measure brain activity involved in voluntary movement preparation, initiation, and execution. In the study, the researchers specifically used BCI to measure the brain activity of participants as they executed a self-initiated movement and attempted to veto the movement. Specifically, the participants were instructed to press the pedal when the monitor showed a green light to win points and not press the pedal at red light [11]. 

Utilizing this experimental setup, the study was divided into three stages [11]. In the first stage, the red stop light was shown at random times to make participants' movements unpredictable and Electroencephalograms (EEG) recorded the spontaneous electrical activity of the brain. In the second stage, a BCI was trained to predict participants' actions and trigger stop signals to interrupt said movements in a nonrandom pattern based on the participants' EEG, without the participants being informed that the pattern of stop signals was changed. In the final third stage, the procedure was the same as the second round, but this time participants were informed that the brain-computer interface would try to predict their movement and interrupt them with red stop signals based on the participant's movements in earlier stages [11]. 

After analysis of the results, the study found that participants were 50% more likely to press the button after a red stop signal when the Brain Computer Interface was actively predicting the participants [11]. This suggests that participants’ brains were actively predicting and anticipating movements based on prior experience. Moreover, the study found that, on average, cancellation of an unconsciously initiated movement was possible if the veto signal occurred before a point of no return of approximately 0.2 seconds following the onset of the readiness potential. If the veto signal occurred more than 0.2 seconds following potential readiness onset, the movement went to completion and participants could not cancel the upcoming movement [11]. 

The experiment's results suggested that while the brain relies on predictive and anticipatory processes to guide human behavior, it still can exert some conscious control over the actions initiated by unconscious cerebral activity via a veto mechanism [11]. More importantly, the finding of the "point of no return" in vetoing self-initiated movements indicates that there are limits to our control over our actions, wherein brain processes may partially control our actions. Nevertheless, some may see the temporal limitations of the veto mechanism as evidence against free will, arguing that unconscious brain processes beyond our control predetermine and compute our actions, leaving little room for the conscious will to decide. On the contrary, others might argue that the veto mechanism shows the role of the brain in conscious decision-making and agency, therefore supporting the pro-free-will argument that we indeed have some degree of control over our decisions and actions. Ultimately, the study indicates conscious modification or cancellation of an action after its onset is possible in the right time frame.  

Using the past to anticipate the future

A concomitant study examining motor control over self-initiated movements was conducted by researchers Alexander, Schlegel, Sinnott-Armstrong, Roskies, Wheatley, and Tse, who sought to examine the role of readiness potential in decision-related or anticipatory processes that are non-motoric [12]. The results of the study showed that the RP was influenced by non-motoric processes, such as the level of attention and the emotional valence of the task. The authors of the article discuss the implications of this finding for our understanding of the neural basis of voluntary action and the role of non-motoric processes in shaping the RP. Notably, the study utilized a novel task to isolate motor and non-motor contributions to the RP, showing that robust RPs occur in the absence of movement. Using this approach, the study showed that motor processes do not significantly modulate the RP, which suggests that the RP is unlikely to reflect preconscious motor planning or preparation. RP may instead reflect decision-related or anticipatory processes, which contradicts Libet’s study. Consequently, this raises the question of whether readiness potential is an accurate measurement of unconscious brain activity and to what extent unconscious brain activity is responsible for motor planning, preparation, and execution of voluntary movements [12].

Fascinated by this question, researchers Reznik, Simon, and Mukamel sought to examine the role of stimuli-anticipating and planning processes by investigating the sensory consequences of voluntary actions on presence of readiness potential [13]. The study set out to understand whether readiness potential related to upcoming voluntary actions reflects preparatory motor activity or anticipation of sensory stimuli. To answer this question, researchers recorded EEG data from 14 participants performing self-paced button presses. In a motor-sound condition, when participants pressed a button with one finger, a sound was triggered. In a motor-only condition, pressing a button did not trigger any sound. In the sound-only condition, the participants were exposed to externally generating sounds in anticipated timings. The results of this study showed that the amplitude of readiness potential in the motor-sound condition was much more negative than in the motor-only condition, suggesting that the participants anticipated an upcoming auditory stimulus. Overall, the study indicated that our brain predicts the sensory outcomes of an action before it is completed, challenging the notion of conscious free will [13]. Therefore, human decisions may not be fully volitional and free, given that actions are, at least in part, regulated by the brain's anticipation and expectation of the action’s sensory outcomes.

Similarly, the role of readiness potential in sensorimotor processes has also prompted researchers Vercillo, O’Neil, and Jiang to investigate the role of sensory-motor activity in predictive mechanisms of human voluntary actions [14]. The researchers recorded electroencephalogram data of 15 participants in 100 motor condition trials requiring a simple action, 100 visual condition trials involving a presented visual stimulus, and 100 visuomotor condition trials requiring a button to be pressed for a visual stimulus to appear. The study measured brain activity before a motor act and/or after a visual stimulus was presented. Premotor and visual cortex regions were found to respond differently to intentional actions compared to actions in response to stimulus. The results showed that premotor brain activity, namely the readiness potential, is affected by stimulus expectancy. The brain alters its response to stimulus based on the type of action performed and the consequence of the action. When an initial movement is performed, there is less response to sensory information from the movement compared to when the sensory information is received from external stimulus prompting us to perform an action. Thus, the researchers argued that the amplitude of readiness potential changes in response to anticipation of a visual feedback following a voluntary action. These results further support the argument that premotor brain activity in the form of readiness potential actually indicates predictive and anticipatory processes in the sensory-motor systems of the brain. The study also highlighted that our perceived sense of control and free will over actions is not simply because of free and conscious decisions, but also because of unconscious preparatory and anticipatory processes that control and predict sensory outcomes of our movements [14]. 

While the previous research highlighted stimulus anticipatory and predictive processes crucial to human volition, researchers Phillips and colleagues were particularly interested in seeing how the processing of past decisions and stimuli expectations in the prefrontal cortex influence the execution of voluntary decisions [15]. Using magnetoencephalography to measure the magnetic field generated by the electrical activity of neurons, the study examined voluntary decisions between two equally appealing options, wherein 20 participants pressed a button to choose a single filled circle or multiple filled circles without any reward or feedback. This allowed the researchers to study the relationship between activities in different brain regions, the degree of uncertainty or randomness in the stimulus received, and the uncertainty in the decision made. Researchers found that the activity in the frontal and the temporal lobe are related to randomness and uncertainty of past decisions, highlighting that people’s past actions and decisions guide their present and future ones. The study found that the brain’s response to the variability of the previous experience determined the degree to which a person’s behavior was influenced by their recent experience. On the other hand, the study found that before a decision is made, the randomness of a choice is processed in the right front region of the brain, associated with learning or retrieving rules. However, after the decision was made, researchers found activity in the left front region of the brain. This result suggests that people utilize specific guidelines and conditions that determine the timing or sequence in which actions or events occur to help them make a decision. Ultimately, the results of the study indicate that human volition and conscious free will is not the only thing driving and executing movements, but rather, the machinery of our brain utilizes past experiences and actions to compute and prepare decisions for future situations [15]. 

More recent research pursuing the link of neural activity to preparation and promotion of voluntary actions was conducted by researchers Travers, Friedemann, and Haggard, who also studied the role of readiness potential in planning and anticipation of voluntary actions [16]. The authors argue that external factors, internal volitions, and stored knowledge all concurrently influence our actions. However, the meaning of this pre-conscious neural activity is still controversial, with some studies proposing that readiness potential is a sign of voluntary actions being generated internally. In contrast, other researchers argue that readiness potential reflects the planning process and temporal expectations. However, in past studies, actions weren’t influenced by external stimuli, which introduced elements of preplanning and anticipation. To distinguish between conscious will from anticipation and preplanning of action, the researchers used a reinforcement learning technique to study changes in readiness potential in response to how participants learned through trial and error. The study presupposed that if readiness potential reflected conscious will, the magnitude of readiness potential should be the highest early in learning, when participants cannot anticipate how to act and the lowest when participants learned to anticipate and plan an action. The results indicated that the readiness potential increased with learning, suggesting neural activity reflects planning and anticipation of an action rather than free will acting independent of external influence. Thus, the authors argue that readiness potential is not a sign of internal generation of action as was previously believed but is actually a result of cerebral planning and anticipation derived from previous experiences [16]. 

It is evident that ample studies have highlighted preparatory and anticipatory influences in human volition by gathering evidence to support Libet’s deterministic view of conscious free will as lacking any causal role in decision making. Nevertheless, it was not long before Libet’s deterministic view was challenged by a study conducted at Caltech by researchers Maoz, Yaffe, Koch, and Mudrik, exploring the relationship of readiness potential with arbitrary and deliberate decisions to uncover the elusive causal role of free will in decision making [17]. Undeniably, previous research was strictly limited to examining the implications of the RP for the causal role of conscious will in arbitrary and simple decisions, failing to consider the role and implication of RP in deliberate, contextual decisions. For instance, previous studies focused on arbitrary and spontaneous actions such as moving a hand from right to left or randomly pressing a button that were purposeless and had no real consequences. This contrasts sharply with numerous real-life deliberate decisions thatreasoned, purposeful, and bear real consequences, such as which clothes to wear, what to eat, how to interact with others, as well as constructive decisions about life partners, education, and career choices [17]. 

To contrast the two decision types, the study compared the causal role of the readiness potential and conscious will in both deliberate and arbitrary decisions in 360 trials in 40 sections [17]. Participants were asked to rate each of the 50 non-profit organizations on a scale of 1-7. In deliberate blocks, subjects were instructed to choose the nonprofit organization (NPO) they would like to donate $1000 to by pressing either Q or P button on the keyboard, and were informed that one of their choices would be selected randomly to advance to a lottery. The participants were incentivized to prefer one NPO over another by showing a signed affirmation to donate the money. In arbitrary blocks, subjects were told a pair of NPOs in a randomly selected trial would proceed to the lottery together. Participants had no incentive to choose one NPO over the other, as both NPOs would receive a $500 donation each, regardless of whether the participant pressed P or Q. The study found the anticipated RP during arbitrary decisions, but surprisingly RP was not registered for deliberate decisions. Because RP did not precede deliberate decisions, these results, combined with diffusion model, suggest that RP onset likely represents accumulation of random neuronal noise and fluctuations that control arbitrary decisions but not deliberate decisions. The findings of this study indicate that RP may not be a true marker of unconscious decisions that produce voluntary actions and, therefore, results from Libet-type studies are not necessarily generalizable to deliberate, contextual decisions that we make in oureveryday lives [17]. 

While the majority of neuroscience studies seeking answers to human volition and free will limited their scope to self-initiated decisions and movements, researchers Park, Barnoud, Trang, Kannape, Schaller, and Blanke expanded the scope of the field by investigating the implication of internal bodily signals of breathing for voluntary action and readiness potential [18]. The researchers found that people systemically start voluntary actions more often when exhaling, suggesting a relationship between respiration and conscious will and motor cognition. Moreover, the results indicated there is no respiration-action coupling when actions are initiated by external factors or stimuli rather than by the person's own voluntary decision, and the magnitude of readiness potential changes based on the respiratory phase. Moreover, these findings indicate that readiness potential is related to fluctuations of continuous neuronal activity driven by involuntary and cyclical respiration. The results suggest that spontaneous respiration affects an essential component of conscious will and motor cognition, as measured by voluntary action and readiness potential. Researchers propose that cerebral processing of breathing is a substantial source of ongoing neuronal fluctuations that emerge as readiness potential. Overall, the results of the study indicated that breathing is coupled with the manifestation of readiness potential and that this coupling was stronger for voluntary actions that required more effort [18]. 

While confirming that the onset of readiness potential during voluntary actions is representative of neuronal activity fluctuations caused by respiration, the study also addressed the question raised by Libet regarding the relationship between perceived intention to move, readiness potential, and unconscious cerebral activity [18]. Thus, the study argues that readiness potential does not relate to the unconscious initiation of voluntary action, instead suggesting breathing-related brain activity is related to initiation of volitional action. This processing implies that the fluctuations in neuron activity preceding the onset of voluntary action are not only spontaneous noise, but are also related to a person's breathing cycle. Ultimately, these findings support recent proposals that the readiness potential reflects random fluctuations of ongoing neural activity driven in part by breathing, rather than the brain’s unconscious decision to perform an action before a person becomes aware of it, as Libet argued [18].

Free will, two ways

By now, there was a clear emergence of two competing interpretations of conscious free will, wherein some researchers argued for a willful and internally-driven model of volition, others supported the external, uncertain decision interpretations of volition. This long-standing divide has prompted researchers such as Travers and Haggard to more closely examine the elusive role of readiness potential in human volition [19]. They did this by comparing the two prominent explanations of free will by conducting an electroencephalogram recording of 20 participants performing a sensory task. Here, participants decided to either accept or reject 300 gambles displayed on a roulette-style wheel consisting of easy decisions, difficult decisions, and guesses. The study found that people are more likely to accept a gamble if there is less uncertainty or difficulty between making a choice, higher chance of winning, and higher reward. The results also showed that readiness potential was unaffected by different levels or strengths of evidence and decision certainty. These conclusions suggest that there are two parallel neuronal pathways involved in initiating a movement - some actions are self-initiated and some are based on sensory evidence. Because the motor preparation activity in the brain was higher before voluntary actions, the researchers argue that readiness potential reflects internal, willful generation of an action rather than random fluctuations or conflict during a decision. Combined, the results oppose earlier theories linking readiness potential to uncertainty or conflict in voluntary decision making. Instead, the study provides evidence to suggest that voluntary, internally generated actions are more self-initiated, preplanned, and predictable rather than random, conflicted, and uncertain [19]. 

Overall, it was clear that the primary focus of leading research efforts on human volition lay within the frontal region of the brain, known to be crucial for voluntary movement, expressive language, and higher-level executive functions. However, British researchers Khalighinejad, Garret, Priestley, Lockwood, and Rushworth did not want to limit such a complex and integral faculty as human volition to just one region of the brain. Namely, the researchers were fascinated by the role of an evolutionarily old brain structure above the thalamus, called the habenula-insular circuit, in the voluntary behavior [20]. To examine the willingness to act, the study defined the concept as the likelihood of making a decision based on the context within a situation. The experiment then followed 25 participants who were tasked with watching a nature documentary and given chances to make effortful decisions to receive rewards while their head was scanned by MRI machine. Participants took into account contextual factors like the probability of winning or the magnitude of the reward, and could choose to complete a force exertion task to receive the reward or continue watching the movie uninterrupted [20]. 

The use of MRI scans revealed that two specific brain regions were crucial in the decision making process [20]. The habenula region was found to be crucial in tracking the variation in "willingness to act" from trial to trial, while the anterior insula region was crucial in encoding the specific contextual factors that determined the willingness to act. Combined, the study proposes a multi-level network of brain activity that helps determine whether the decision to act is executed or not, wherein the anterior insula region encodes the sensory context and integrates various sources of information before the information is passed to the habenula. Once the habenula receives the sensory context and information, it tracks and sorts the variation within the information and guides the decision-making process. Ultimately, the processed information is sent to the supplementary motor area to make the final decision. Overall, the results of this study most closely align with the deterministic view of human free will and volition, wherein conscious human decisions and willingness to act are not fully random, internal, and voluntary. In addition, the study supports the view that the human brain takes into consideration contextual information and circumstances combined with previous actions to at least in part compute, guide, and predetermine human actions and decisions [20]. 

Concluding remarks and discussion:

Without robust scientific methods and tools, thinkers of the past have relied on philosophical means to define and understand free will and consciousness. Nevertheless, the capricious and elusive nature of free will and consciousness stumped even the greatest philosophers, thinkers, and scientists, who have all failed to agree on a definitive answer to the innate human faculty underlying every human endeavor. However, by the mid 20th century, neuroscience had progressed far enough to allow humans to approach human consciousness from an empirical perspective. Decades worth of research has shown that neuroscientists can detect unconscious brain activity accompanying upcoming voluntary movement and can infer both the timing and decision of your action several seconds before one is consciously aware of the choice. 

Ultimately, this matter is not so simple, and human free will cannot be disregarded as an illusion. However, collaborative efforts of neuroscience and philosophy have provided refined insights into free will, providing a better understanding of the role of readiness potential in motoric and non-motoric movements, as well as showing that humans can even consciously modify or even cancel upcoming actions. While the results of studies conducted by Libet and his proponents indicated that voluntary movements are, at least in part, planned, prepared, and initiated by unconscious processes, most of these empirical studies also focused on arbitrary, irreflective, and spontaneous actions. Some might argue that such actions like walking and even riding a bike are done so frequently that they might become primarily automatic and intuitive, requiring little to no conscious deliberation. Many actions in our everyday life can be classified as such, wherein they are arguably done so routinely that our brain might learn to anticipate those actions and plan how to initiate and execute them unconsciously [14][15]. This would be more efficient than having to deliberate on an arbitrary and insignificant task consciously. However, opponents of this view would argue that our consciousness and free will might be preoccupied with arguably more meaningful choices and decisions, such as deciding on a job, choosing a place to live, finding a life partner, or solving a difficult exam. This distinction between decision types is suggested by the difference in the brain activity present when a person does an arbitrary and meaningless task versus a deliberate and meaningful task. Namely, research has indicated that readiness potential is present during the meaningless task, as is expected by researchers like Libet, but is surprisingly absent during meaningful and deliberate choices. Nonetheless, the work of researchers like Libet, who uncovered unconscious brain activity behind volition and voluntary movement, is helping uncover new ways to understand and approach addictive, impulsive, and criminal behaviors. Research highlighted the potential role of unconscious brain activity in anticipating, preparing, and initiating certain voluntary actions, suggesting that addictive, impulsive, or even criminal behaviors may be brain disorders driven by uncontrolled unconscious processes instead of a lack of willpower or control.

Thus, while it may be true that our free will may not fully extend to and control every decision or action we make, it does not bar us from having willful and conscious control over actions and decisions that are meaningful for our lives. Moreover, it is important to note that just because some human decisions and actions correlate with unconscious brain activity, such as readiness potential, we are not by any means definitively deprived of free will and are subject to spontaneous neural fluctuations and activity. Proponents of free will would contest that the brain and its activity are not separate machinery or entities from ourselves, our identity, and our mind. On the contrary, one can argue our brains, and the brain is an integral part of us. In truth, the nature and workings of our brain are yet too complex, enigmatic, and elusive for us to make definitive ultimatums on these topics, such as by disregarding the existence of free will and the conscious self. Ultimately, consciousness and free will currently do and will continue to guide, inspire, and support us in our profound philosophical and neuroscientific pursuit of better understanding our brain, mind, and ultimately ourselves.

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