Perception . . . Dr. Satcheu

"This pathway, it is held, went on Dr. Satchell, "becomes easier to traverse through repetitive activation; activity in this pathway impresses upon it some enduring structural or physiological change so that an impulse begun at the start of the chain will tend from then on to follow it out to completion." Of crucial importance to this theory was the question of whether activity at the synapses, the junctions between cells, did influence in any way their ability to transmit activity subsequently.

"A particularly favourable anatomical situation in the spinal cord in mammals has enabled this point to be verified experimentally. Between some of the ingoing and out-going nerve fibres of the spinal cord there is only a single set of synapses. It is thus possible," continued Dr. Satchell, "to stimulate the incoming nerve and to measure electrically the amount of activity that emerges in the outgoing nerve, after having traversed a synapsis." It had been clearly demonstrated that even in synapses busily engaged in the normal traffic of the body, a prolonged burst of activity increased their ability to transmit activity for a period of three months or so. If the synapses were artificially kept silent by cutting the incoming nerve, then periods of increase of several hours could be shown.

In the classical point of view, it was to be expected the memory traces or engrams would be localised in some specific part of the cortex. "Let us examine the evidence for and against this." said Dr. Satchell. In favour the following three pieces of evidence could be cited. Firstly, in conscious human subjects, electrical stimulation of certain specified areas in the temporal lobe would induce either a recall of long past and forgotten memories or an alteration of the perception of present experiences. Particularly common in the latter case were "deja-vu" phenomena.

Secondly, monkeys, in which both temporal lobes had been removed, showed a gross alteration in their perception of things; though normally frightened of snakes, they would ignore a snake in their cage. Though normally vegetarian, they would eat meat.

Lastly, human beings who had had one or other temporal lobe removed, showed specific defects. If left without the right temporal lobe, they failed to detect anomalous situations portrayed on picture cards. This indicated certain defects in perception. If minus their left temporal lobe, they showed certain characteristic defects of recent memory. All this seemed to suggest that the temporal lobes were in some way concerned with recording memory, though the engrams could not be stored there, since people with both temporal lobes removed or damaged did not show complete amnesia.

Against the classical view, the work of Lashly could be cited. Groups rats trained to solve mazes had different parts of their cortex removed. From a long series of such preparations, Lashly concluded that it did not seem to matter which part of the cortex was removed, but only how much of it. The cortex appeared to be equipotentis. The number of successful scorings in solving the maze was much the same in the various groups in which 10% of the cortex was removed, no matter which part constituted the 10%.

The work of Sperry, in which the inability of the cat to transfer memories of feeding patterns from one hemisphere of the brain to the other after the transverse linking fibres had been [unclear: cut] could also be cited here. In this [unclear: pre] paration, transference could occur [unclear: as] long as even a 2 mm. strip of the [unclear: fibres] remained. It did not matter [unclear: which] purl of the commissure was included [unclear: in] the 2 mm. strip.

Whilst the removal of parts of [unclear: the] human cortex caused certain [unclear: subtle] changes in personality, there was [unclear: no] indication that specific blocks of [unclear: memory] traces were eliminated, or that the [unclear: ability] to memorise was damaged as long [unclear: as] the temporal lobes were spared. All [unclear: this] seemed to suggest either that [unclear: the] classical view was correct but that [unclear: every] engram was written into the cortex [unclear: is] many different places, or that the [unclear: whole] view was untenable.

Changes in the type of [unclear: inter] connections between large groups [unclear: of] cells would be expected to alter the [unclear: type] of pattern shown. The repeated [unclear: estab] lishment of any one pattern would [unclear: ten] to make it more likely that such a [unclear: pat] tern would form in the future. "[unclear: This] type of exploration," concluded [unclear: Dr.] Satchel), "in which a memory [unclear: trace] represented as a pattern of firing [unclear: in] volving the cortex as a whole has [unclear: the] merit that the removal of part of [unclear: the] cortex does not prevent the [unclear: establish] ment of the pattern around it."