Differences on “Awareness of willing to act” and “Readiness Potential” components in voluntary actions in bulimia nervosa

Voluntary actions are preceded by neuro-electrophysiological “Bereitschaftspotential (BP) or Readiness Potential” (RP). The Readiness Potential (RP) is a slow negative shift in neuro-electrical potential generated by the brain that begins at about a second or more before a self-paced voluntary motor act. Benjamin Libet’s famous experimental findings led us to conclude that voluntary acts can be initiated by unconscious cerebral processes before any conscious “willing or intention to act” appears. This empirical finding strongly challenges the old notion of “free will” which argued that the conscious intention or free will initiates the onset of the specific cerebral processes that mediate the act. Later researchers have found that RPs were absent or reduced in brain illnesses like Parkinson disease and some mental disorders like Tourette’s syndrome. Based on Libet’s method, the present study aimed to examine the differences of Readiness Potential’s components (Peak and latency) among persons with bulimia Nervosa compared to the control (normal) group. Also, this research investigated and compared the perceived time of willing to action (W time) and the perceived time of action itself (M time) between the groups. Bulimia nervosa, as a mental health condition and an eating disorder, is characterized by eating much food and then taking inappropriate steps to prevent weight gain, such as vomiting or misusing laxatives. People living with bulimia feel that they are not in control of how much food they consume during an episode of binge eating and subsequent purging, which usually occurs at least once a week. Binge eating refers to eating a large amount of food in a short amount of time. Purging refers to the attempts to get rid of the food or calories consumed.

Thirty-six subjects (19 with bulimia and 17 normal) participated in two 40- trial blocks. In the two blocks, subjects were asked to press a key at any time they felt the “willing” or desire to do so. In the first block, subjects reported the perceived time of will to act of pressing the key, (W) and in the second block, they reported the time of pressing the key itself (M). Reports of W time (in the first block) and M time (in the second block) depended upon the subject’s recall of the spatial Libet’s clock- position of a revolving spot at the time of her/his initial awareness of doing (M)/intending (W) to press the key. During all procedures the 64-channels EEG was recorded.

Results showed that no significant differences in “W time” and “M time” between the groups. Nevertheless, EEG data from the “W block” showed a significant difference between the bulimia and normal groups in the “peak component” of CP1, CP5 and PZ Channels. Peak components of these channels were more significant in the bulimia group than in the normal one.

As these significant channels are related to the parietal lobe, and the parietal lobe is related to awareness of willing to act, the current study’s findings show that the awareness of will and intention to act among persons with bulimia nervosa is disturbed at the neuroscientific level.