Ever since the recording of history began, the concept of consciousness has baffled many great thinkers, from many different fields such as philosophy, psychology and neuroscience to name a few. Questions such as understanding of how our mind works, what is it, to where it is located has repeated itself over time. René Descartes (1596-1650) was the first to not only make a clear distinction between the physical abilities and mental processes, called dualism, he was also the first to acknowledge the brains role in sensory input and output.
Thus, becoming the first to attempt a systematic approach to the study of consciousness. Descartes believed that the source of our consciousness and all it entails to have a conscious experience was due to the involvement of the pineal gland. In his attempts to explain the importance of this he suggested that perception came from hollow tubes of thin nerve fibres which would stretch into valves in the ventricles connecting them to sensory organs. And a stimulation of the organs would set them in motion creating perception. He also believed that these hallowed tubes were filled with animal spirits (Lokhorst and Kaitaro, 2001).
Although he’s theories has been rejected today the distinction between physical properties and mental processes made by Descartes is still important. This due to the fact that the main aim in neuroscientific research today is to understand the relation between physical properties and mental processes and how it results in conscious experience (Brogaard and Gatzia, 2016). Few accept dualism as a solid theory of consciousness today, and after Descartes numerous theories has risen to attempt to explain the concept of consciousness, however, the majority is not accepted as valid theories today. Today, when studying the neural correlates of consciousness (NCC) it is very much based on the idea put forward by Julien Offray de la Mettrie (1705-1751); that the concept of consciousness itself is far more complex than the result of simple involuntary and instinctive processes, and that “the mind somehow emerges from the physical properties of the brain” (Schneider and Velmans, 2017, p. 3). A conscious experience is our awareness of ourselves, what we do, how and when we do it, whether you are having a cup of coffee, watching the sunrise, smelling the flowers in your garden or dreaming, you are having a conscious experience. Defining consciousness itself is difficult as it is an ambiguous term and depends on the approach we choose to take.
The term consciousness is ambiguous due to not only being a broad term across different fields, such as it in some cases can be used interchangeably with mind, but also because it is dependent upon the amount to which we experience consciousness. Thus, the amount of consciousness we experience vary between being awake, sleeping, dreaming, the level of consciousness present in permanently vegetative patients (PVC), and the amount of mental processing occurring without conscious awareness (nonconscious) (Velmans, 2009). Therefore, it is easier to define the concept once there is a generalized agreement on its phenomenology and an approach to study can be taken. Consciousness can be studied either through subjective reports, objective measure, or a combination of the two, to which the latter is more common within academic fields (Schneider Velmans, 2017).
In 1964, Benjamin Libet made a significant discovery that resulted in him becoming a pioneer in the field of consciousness. Libet (1964) conducted a study on neurosurgical patients which had to remain awake during the procedure due to clinical reasons. After receiving local anaesthetic to the incision points on the skull, different trains of electrical pulses were administered to the patient’s postcentral gyrus (somatosensory cortex). The patients were asked to report if they felt any form of sensations and the limited threshold where they reported sensations were between 0.5 to 1 s. The amount of sensation the patients reported they felt were dependent upon the frequency of the stimulus pulses. So, if the frequency were turned up to 15 Hz for 0.1 to 0.5 s, the sensation the patients felt went from simple tingling to feeling the need to draw the hand away. Furthermore, if they increased the intensity up to two seconds, they observed muscle twitches without the patient’s awareness, other times they would report feeling muscle twitches. Libet reported that it took the patients up to 500ms after the electrical train of pulses had begun to consciously be aware of the sensation. These findings gave birth to the facilitation hypothesis, which states that a stimulus which is low in its intensity will take longer to create a conscious sensation than a stimulus high in its intensity. These findings indicate that upon feeling touch on our body, the brain has a large evoked potential followed by continues firing. Taking the delay of conscious awareness of the sensation into consideration, it raises the question if we are consciously experiencing the world in a form of delay (Libet, 1964).
During a study by Libet et al (1983) participants were asked to flex their wrist when they felt the urge to do so. At the same time they were watching a clock on an oscilloscope, rotating 1 revolution every 2.6 seconds. They were then asked to report the position of the clock upon which they felt the urge to flex their wrist. They then compared the readiness potential (measures of activity in the motor cortex and supplementary motor area leading up to voluntary muscle movement), which is thought to be generated in the SMA. They found that the brain began to prepare movements long before the participants became aware of their conscious urge to move. This suggests that although we feel like we consciously decide when to move, such a decision has already been initiated in the brain long before, because the RP comes before the conscious urge to move. The decision of when to move happens unconsciously in the brain.
Haggard and Eimer (1999) conducted an experiment similar to the original libet experiment, but here the participants could press with either their left or their right hand. This allowed them to calculate the lateralized readiness potential (LRP) which shows the degree to which they have activated one response over the other. They found that the LRP began around 700ms prior to movement, while the participants judged their urge to move at around 300ms prior to movement.
Soon et al (2008) conducted a study using fMRI imagining to record the brain activity leading up to a decision. They had their participants watch a sequence of letters on a screen and could freely choose to press a key with either their left or their right hand. They were then asked to report which letter was on the screen when deciding which button to press. They could decode from the activity in the participant’s frontopolar cortex which button they were going to press 10 seconds before they became consciously aware of this decision. In fact, activity in the SMA preceded the decision by 6 seconds, and from this activity they could 5 seconds prior to the decision decode which button the participants would press. This suggests that activity in the prefrontal regions are responsible for the initial decision regarding which button to press and this decision is then passed to the SMA and then to the primary motor cortex. Together with the results from Libet (1983) and Haggard and Eimer (1999) these results provide compelling evidence that both the what decision and when decision occurs unconsciously in the brain.
Filevich et al (2013) studied unconscious inhibition where in the instructed condition participants had to either press a button immediately or delay their response and press later (initially inhibiting responding to the stimulus). And in the free condition they could choose freely to press now or delay. Activity in the premotor cortex prior to the stimulus appearing was predictive of whether or not people decided to inhibit (delay) their button press. This suggests that even freely selected whether or not to execute intentional action are influenced by unconscious brain activity.
Our experiences tells us that we have conscious free will, meaning that “we” decide out actions. Wegner and Wheatley (1999) decided to test how easily this could be manipulated. They had two people, one participant and one confederate place their hands on a keyboard attached to a computer mouse. The participant were told to move around the screen and stop on whatever object they wanted. In reality it was always the confederate that chose when, and therefore where, to stop the mouse. The participants were played a sequence of words which they were told were irrelevant. When they heard the name of an item, immediately before stopping on that object, they (wrongly) judged that they had chosen to stop on that object. This shows that conscious thought (intention) prior to an action is enough to trick people into believing that they had conscious free will in their choice of action.