The Preservation of Consciousness, Automatism, and Movement Control

SIR: The paper by Devinsky et al.¹ contains important laterality indexed information concerning the preservation of consciousness, automatism, and movement control, which deserve to be put in a more cohesive perspective. This in turn could have helped to present the data in a more scientific manner. Specifically, I am referring to the works of Serafetinides² on the role of the major hemisphere in preservation of consciousness and Serafetinides and Falconer³ on the role of the right (minor) hemisphere in speech automatism. The results of these large numbered and meticulously conducted studies have been confirmed in more recent times,^4,5 all indicating that when a seizure occurs with speech arrest, loss of consciousness, and presence of memory of preictal events, the lesion is in the major hemisphere. As these authors recorded epileptiform EEG activity in such patients the process is epileptic by definition, and calling the process convulsive is appropriate in those in which actual convulsion is seen (majority occurring in major hemispheric lesions). To a neurologist, “nonepileptic seizure” is an oxymoron. Of course, “hysterical seizures” do occur, but if the behavior is associated with the rest of the items enumerated above and is seen with a brain lesion in either hemisphere, one must avoid using that confused and confusing terminology.

The role of laterality of movement control (alluded to above, and codified in handedness) in maintaining the stream of conscious awareness is becoming clearer. The activating neuronal aggregate devoted to voluntary movements (otherwise called the command center in the major hemisphere) has been recently the subject of an investigation based on a review of the literature and my own data. This ensemble mediates interlimb coordination, guaranteeing the existence of a cohesive self in a brain consisting of two hemispheres. It is only when this asymmetrical interhemispheric relationship is disturbed, such as in surgical callosotomy, Marchiafava-Bignami disease, and traumatic or vascular callosotomy, that the cohesion is lost forever. Cases of ictal automatism, as mentioned above, are instances representing temporary disruption of this cohesion. All references cited indicate that only when the activating moiety (within the major hemisphere) is involved in the epileptogenesis will the person lose consciousness, as the disruptive process is conveyed to the remaining hemisphere via the callosum. Epileptic activity generated within the minor hemisphere is the source of automatisms only, as mentioned above. It cannot be generalized because the callosal traffic for movement is one-way only. This recently described anatomy forms the neural basis for handedness.⁶ One of its manifestations is the melody lead of the piano players that has been known to musicologists for more than a century. The reason for the delay of all effectors on the left side (in right handers) is the time taken for the command in the major hemisphere to reach the motor cortex on the right via the callosum.