The Brain and the Hand.
Every representation of a movement awakens in yoga poses some degree the actual movement which is its object. Every pulse of feeling which we have is the correlate of some neural activity that is already on its way to instigate a movement. Our sensations and thoughts are but cross-sections. (William James, 1890, The Principles of Psychology, II, will, 1135)
In his studies on the psychophysiology of relaxation, Jacobson corroborates the idea that the architecture of the organism coordinates thoughts and gestures.
The research that I summarize analyzes the temporal rapport between the brain and the muscles of the right hand when a therapist asks a patient to extend his right hand.
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To study this, Jacobson placed electroencephalograms (EEGs) on the head and electromyograms (EMGs) on the hand. The EEG allows for the detection of the regions of the brain where there is activity, and the EMG allows for the detections of small muscular contractions, indiscernible to the naked eye, to touch, or by introspection. 6
Typically, people expect that the instruction to move the hand first activates the brain (activity detected by the EEG) and then the muscles of the hand (detected by the EMG). This sequence is often observed in yoga poses an experimental situation in yoga poses a laboratory where all the interventions have been prepared in yoga poses advance with the subject. It is reversed when there is a sensory irritation (excitation of the retina, pain caused by a flame, etc. ). Jacobson quotes a few neurological studies of his time (before 1967) that show cases where an instruction given to a subject activates the brain and the hand of the patient simultaneously. He concludes that there are circuits that integrate the peripheral activity (linked to the muscles and to the skin) and the central (brain) nervous system.
Jacobson confirms this hypothesis with studies that tested the temporal coordination between the activity of the hand and the brain at the occasion of a voluntary act. The experimenter asks his subjects to feel their right hand. He observes that in yoga poses the situations he has created to control this variable, the EEG and the EMG begin plotting simultaneously. These results confirm the hypothesis that the coordination between voluntary movements and thoughts is regulated by organismic circuits, but these studies have not been sufficiently replicated to be considered robust. To my knowledge, they have never been invalidated, even if Jacobson's instruments use a temporal scale somewhat too large to be conclusive.
Jacobson also shows that even with subjects experienced in yoga poses relaxation, it is impossible to think of a hand movement without generating a slight mobilization of the muscles involved in yoga poses the movement.
This confirms the hypothesis that a thought is part of a mechanism of organismic regulation, and is never an isolated event. Jacobson distinguishes (1) thought, (2) the mobilization of the hand, and (3) the mechanisms that coordinate hand and thoughts.