192 SECTIONAL ADDRESSES. 
we must guard against the notion that such high-level activity implies a 
narrowly-limited zone of mental processes. On the contrary, it implies 
a wide sphere of activity rather than a punctate, pineal gland-like soul. 
It follows, therefore, that we cannot hope to localise any act or any 
content, of consciousness in one small region of nervous substance. Afferent- 
efferent localisations of function undoubtedly occur—regions where the 
incoming impulses become deflected to outgoing processes : our knowledge 
of the physiology and structure of the spinal cord clearly points to this. 
Sensori-motor localisations may, in a sense, be said to exist similarly in the 
brain. The occipital region of the cerebral cortex, for example, is 
concerned with vision. But because vision ceases when the area 
striata in this region of the cortex is injured, we are not justified in 
saying that this area is the seat or centre of our visual consciousness. 
All that we are warranted in concluding is that it is essential for our 
visual consciousness, that without it vision is impossible—a very different 
statement. 
Once again, let me repeat, consciousness implies self-activity. There 
are no separate loci for different kinds or modes or qualities of conscious- 
ness. The nervous system and the system of self-activity works as a 
wide-spread unity. Different regions of the brain are more particularly 
concerned in giving rise to certain kinds of consciousness. The 
thalamus, for example, is especially concerned with the emotional 
consciousness ; but we are not justified in calling it the seat or centre 
of such consciousness. 
It is impossible to localise consciousness. There are no specific ‘ mental ’ 
symptoms diagnostic of cerebral tumours in different regions of the brain. 
The work of recent experimenters’ suggests that the more complea skills 
depend for their acquirement on the activities not of any particular 
cortical area but of wide areas of cerebral tissue. The larger the area 
of brain destroyed, the slower is the rate of subsequent acquirement of 
such skills, and in the rat, at least, this seems independent of the locus 
of the lesion. The same conditions appear to hold for the destructive 
effects of cortical lesions on complex skills which have been already 
acquired. Various simpler skills, on the other hand, appear to depend for 
their performance on the integrity of isolated mechanisms specific, in the 
normal animal, to definite areas of the cortex ; but after their destruction, 
their functions may nevertheless be taken on by other regions of the 
nervous system. Such skills, once acquired, are hence abolished by 
injuries to some particular cortical area, but to no other area. Never- 
theless, in the rat the destruction of that particular area does not appear 
to affect the subsequent acquisition of the simpler skills, and there is no — 
relation between (a) the magnitude (within certain limits) or the locus of — 
wide cortical injury and (b) the ease of such acquisition. Doubtless the — 
number of such localised mechanisms increases pari passu with mental — 
evolution, and at the same time their diffuseness diminishes. But the 
number of possible complex skills, involving the activity of wide areas of © 
the cerebral cortex, must simultaneously increase also. 
2 
‘Cf. Brain Mechanisms and Intelligence. By K. 8S. Lashley. ces 
University Press, 1929. 
