Being constantly submerged in a sea of stimuli impinging on our minds we tend to reduce the impact selectively by a shutting-out mechanism. (Irritation and Counterirritation, 193)

McLuhan must have recognized much of his own health condition in the case of ‘Jimmy’ as described by A.D. Jonas in his 1962 Irritation and Counterirritation. Perhaps McLuhan even self-diagnosed his 1960 stroke and repeated blackouts before and after that stroke on the basis of Jonas’ “mechanism”? In this view, these were “autoamputations” of his CNS (central nervous system) acting as “counterirritations” induced by his “living in a sea of subliminal and supraliminal insults” (Irritation and Counterirritation, 12).

Depictions of McLuhan’s state at this time by himself and others have been given in McLuhan’s health 1957-1967. Compare the case of ‘Jimmy’ set out by Jonas:

[Jimmy’s] growing annoyance and irritation became a source of preoccupation to his wife. Her remonstrations to take time off for his family or have some free time for himself were countered with (…) silence. This was the (…) background against which Jimmy developed severe headaches forcing him to consume from five to ten aspirins daily. Repeated medical check-ups failed to provide any clues (…) Alternately he would fear losing his mind or dying from a brain tumor. Applying the hypothesis that the brain will not tolerate excessive stimulation and therefore, in such an instance, will set into motion an amputative process, a certain sequence of events can be predicted. The sensory organs will become reduced in their effectiveness in such a way that fewer and less intense stimuli will filter through. As a further protection the muscles surrounding the skull will tighten to lessen the impact of external blows (…) The intense muscular contractions combined with vascular changes — the characteristics of the clinical picture of a headache — are the visible manifestation of the autoamputative process of the brain [working] to eliminate itself, a form of biological suicide (…) Jimmy would state that (…) he would experience relief if he just could split his head open (…) effectively desensitizing himself to all the outside and internal stimuli. (Irritation and Counterirritation, 97-98)

Here is McLuhan in Understanding Media (43):

With the arrival of electric technology, man extended, or set outside himself, a live model of the central nervous system itself. To the degree that this is so, it is a development that suggests [the need for] a desperate and suicidal autoamputation, as if the central nervous system could no longer depend on the physical organs to be protective buffers against the slings and arrows of outrageous mechanism. It could well be that the successive mechanizations of the various physical organs since the invention of printing have made too violent and superstimulated a social experience for the central nervous system to endure.

And here is Jonas in Irritation and Counterirritation (12):

the CNS has successively surrounded itself with more and more complex organ systems to maintain for itself an optimum state (…) The ultimate crowning of such a development is the advanced intellectual capacity seen in men. But from the standpoint of optimum functional environment for the CNS, man must be considered a failure, because the very degree of advancement has made it excessively vulnerable to constant irritation.