Noticing the areas of the body affected by removal of various region of the brain suggested that parts of the brain mapped out body parts from head to toe in both the somatosensory cortex and the motor cortex. Penfield drew this image of a homunculus (a little man) along the coronal periphery of the cortex.

On the left, the somatosensory mapping shows sensitivity spread over all the body, where the motor mapping has little motor control over the middle of the body, but greatly increased control for the hands.

Penfield was far from the first to see this mapping of body parts in the brain. Here is an illustration from William James' 1890 Principles of Psychology (p.38) showing the cortical area whose "strand of fibres" (today's neurons), some for the same face area as Penfield's, travel through the internal capsule of the hypothalamus to the brain stem and spinal cord.

It has long been known that visual or auditory hallucinations sometimes come to patients with seizures...Similar "psychical" states are sometimes produced, during operation, by electrical stimulation of the cerebral cortex. Those that are in fact hallucinations of things previously seen or heard or experienced, we have called experiential responses.

Twenty-five years ago, one of us reported electrical activation of such phenomena for the first time (Penfield, 1938). A past experience, which had occurred regularly as part of the patient's seizure pattern, was reproduced by electrical stimulation of the cortex of the temporal lobe.

In some cases it could not be proved by witnesses that the experience was from the patient's past. But in most cases he was confident that it came from his previous experience. When the experience was fragmentary, his present awareness might be invaded by no more than a picture.

In addition to the experiential states that we have described above, gentle electrical stimulation of temporal lobe cortex also produced sudden "feelings"—sometimes the feeling of familiarity that clinicians had been in the habit of calling déjà vu,

Because of the association of the temporal cortex with these two classes of psychical phenomena (recall of past experience, and interpretation of present experience) the term interpretive cortex was used for descriptive purposes (Penfield, 1959).

Let us now reconsider these findings. The psychical phenomena that are produced by activations within the areas of interpretive cortex are of two types: (a) altered interpretation of the present; and (b) a state of mind. You may call the latter an experiential hallucination if you like. The true nature of such hallucinations becomes quite clear when the records of the stimulation responses are studied. They are reproductions of past experience.

The remembrance of the original experience and its record may have been modified by dreams and by re-experiencing... But at operation it is usually quite clear that the evoked experiential response is a random reproduction of whatever composed the stream of consciousness during some interval of the patient's past waking life.

We have argued before, that since excision of these areas does not abolish memory, they do not contain the actual record of the past. They are, however, functionally connected with that neuronal record (Penfield, 19586). Since stimulation produces at times detailed recall of past experience in these areas and nowhere else, and since, at other times, it produces a sudden alteration in the patient's present interpretation of things heard or seen, it seems likely that these areas play in adult life some role in the subconscious recall of past experience making it available for present interpretation. This recall makes possible that sudden flash of awareness that things have been seen or heard or experienced before, or that they are dangerous, coming near, or changing pace.

We have argued before, also, that past experience, when it is recalled electrically, seems to be complete including all the things of which an individual was aware at the time; also that, since the events were often unimportant, it seemed likely that the whole stream of consciousness must be so recorded somewhere, quite beyond the reach of voluntary summons (Penfield, 19546).

There is within the adult human brain a remarkable record of the stream of each individual's awareness or consciousness. Stimulation of certain areas of cortex, lying on the temporal lobe between the auditory sensory and the visual sensory areas, causes previous experience to return to the mind of a conscious patient. There is no real overlap between this interpretive cortex and the areas devoted to visual and auditory sensation, no overlap with the zone of cortex devoted to the ideational processes of speech.

In such repetitions of previous experience perceptions are largely auditory, or visual, or both. Time seems to unroll at its normal tempo. The return of the content of consciousness thus evoked, is quite at random, except that there is some evidence of cortical conditioning. The evolving detail is far greater than in memories which can be summoned voluntarily.

This demonstrates the existence of a functional system devoted to subconscious recall of past experience and to the interpretation of present experience. Like the motor and sensory cerebral systems, this functional unit is partially separable from the overall activity of the brain. Like speech, it depends on an acquired system of functional neuronal connexions.

The challenge that lies before clinician and physiologist, electronics expert and psychologist, is this: How are these partially separable functional systems integrated into normal brain activity, and how is this total integration related to the mind? Final understanding of man's own brain and mind may seem very far away, but that is the ultimate goal of investigation. It may well prove to be man's most difficult achievement, to understand himself and the means by which this understanding is achieved.

"THE BRAIN'S RECORD OF AUDITORY AND VISUAL EXPERIENCE", Wilder Penfield and Phanor Perot, BRAIN, VOL. 86, PART 4, December, 1963, pp.596-696

Over four decades later, BRAIN published a review of Penfield's 1963 report...

The subtitle of Wilder Penfield’s paper, written at the age of 72 years, suggests, like the closing bars of Götterdämmerung, the conclusion to a monumental work of outstanding originality but, in Penfield’s case, born not out of Teutonic mythology but from experimental neurology. Penfield had dedicated his first classic monograph, written with Theodore Erickson (Epilepsy and Cerebral Localisation, 1941) to John Hughlings Jackson and Charles Sherrington. Later, he gave the fifth Sherrington Lecture in the University of Liverpool (1958). The introduction to this final summary of his life’s work, based in part on the Lister Oration (1961) and the Hughlings Jackson Lecture (Montreal, 1961) quotes Jackson: ‘he who is faithfully analysing many different cases of epilepsy is doing far more than studying epilepsy’; and almost 100 pages later Penfield closes with the same quotation. The story is of Jackson’s ‘dreamy states’ and of their illumination based on Penfield’s observations over a period of 25 years on experiential hallucinations and experiential responses to focal cortical electrical stimulation. He found these to be both simple and complex; in the domains of language, sound or vision; with the emotional conviction of past experience; and, where factual corroboration proved possible, founded on genuine events now recalled. [I-Phi emphasis] Proustian, therefore, in its scope (and biblical in its resonances of Ecclesiastes 3: 1–8 [For every season...]), this is an account of the cortical substrates for ‘remembrances of past experiences’

"From the Archives, The Brain's Record of Auditory and Visual Experience", Wilder Penfield and Phanor Perot, BRAIN, (2005), 128, pp.449–450

See Marcel Proust's reproduction of a childhood experience when tasting a Madeleine.