Wednesday, July 19, 2017

Reading :: Higher Cortical Functions in Man

Higher Cortical Functions in Man
By A. R. Luria

I'm not actually going to review this entire book—the version I read, the 1966 Basic Books version, is massive—but I do want to touch on the framing. The book is based on Luria's neuropsychological work from the 1930s to the time of writing, and it was a landmark book for the neurosciences, exploding the myth that higher mental functions were associated with specific parts of the brain (the reading center, the writing center, etc.). Rather, Luria argues that these higher functions result from the networking together of different parts of the brain. A disruption of that network—say, a gunshot wound in a specific part of the brain—can interrupt that higher mental function, not because it has destroyed the function's brain center, but because that part of the brain is part of a larger chain. Excitingly, that meant that patients could learn to route around the affected area, reconstructing the chain with a substituted brain area. (If you've read The Man with a Shattered World, you have a concrete example of how such rehabilitation might work.)

Of specific interest to me at present: Luria lavishly credits Vygotsky for the basic insights on which his work is built (and dedicates the book to him). In the Foreword, Luria ties "higher cortical processes" to the "higher mental functions" that Vygotsky described (p.1). Luria bases the generalizations on observations over "the past 25 years" (which would be 1937-1962, since the Russian version was published in 1962, a date range beginning with Luria's internship at Burdenko Institute of Neurosurgery. Luria notes that he "first began his clinicopsychological investigations of local brain lesions more than 30 years ago under the guidance of his friend and teacher L.S. Vygotskii. Much of what is written in the following pages may therefore be looked upon as a continuation of Vygotskii's ideas" (p.2).

Luria continues that line in Section I, "The problem of localization of functions in the cerebral cortex." After reviewing early conceptions of brain localization (e.g., brain centers), he argues that "no formation of the central nervous system is responsible for solely a single function"—rather, there are networked functional systems (p.27). In fact, as was well known, a brain lesion can disturb voluntary performance while leaving involuntary performance intact; Luria argues that the result of such a brain lesion is not loss but disorganization (cf. Leontiev and Zaporozhets). Indeed, Luria argues that
The principal achievement of modern psychology may be considered to be the rejection of both the idealistic notion that higher mental functions are manifestations of a certain 'mind' principle, distinct from all other natural phenomena, and the naturalistic assumption that these functions are natural properties bestowed by nature upon the human brain. One of the major advances in modern materialistic psychology has been the introduction of the historical method by means of which higher mental functions are regarded as complex products of sociohistorical development. (p.31)
He goes on to cite Vygotsky—specifically his book Development of the Higher Psychological Functions, of courseand Leontiev, and "to a certain extent" Janet and Wallon (p.31). Specifically, he notes Vygotsky's argument that "social contaact between the child and adults always lies at the root of such forms of activity as paying attention or voluntary movement" (p.33). This social genesis "determines the second fundamental characteristic of these functions, their mediate structure"; here, Luria uses the example of an external sign such as a knot or note to organize a mental process. Speech, he notes, "plays a decisive role in the mediation of mental processes," a claim that he supplements with a quote by Lenin (p.33). Indeed, he praises Pavlov for recognizing "the 'second signal system,' which is based on speech" (p.34). And:
The fact that systems of speech connections are necessary components of the higher mental functions makes the cerebral organization of these functions an extremely complex matter. We therefore suggest that the material basis of the higher nervous process is the brain as a whole but that the brain is a highly differentiated system whose parts are responsible for different aspects of the unified whole. (p.35)
He goes on to endorse Leontiev's "functional brain organs," which are "formed in the process of social contact and objective activity by the child" (p.35). The "upper associative layers of the cerebral cortex, the vertical connections arising in the secondary associative nuclei of the thalamus, and the overlapping zones uniting different boundaries of cortical analyzers evidently constitute the apparatus that performs this highly complex task. It is in man that this apparatus of the brain has attained its highest development, sharply distinguishing the human brain from that of animals. We, therefore, agree with the view that evolution, under the influence of social conditions, accomplishes the task of conversion of the cortex into an organ capable of forming functional organs (Leont'ev, 1961, p.38)" (p.35).

Luria again credits Vygotsky's insight that "higher mental functions may exist only as a result of interaction between the highly differentiated brain structures and that individually these structures make their own specific contributions to the dynamic whole and play their own roles in the functional system. This hypothesis ... is a thread running through the whole of the book" (p.36). In their early stages, higher mental functions "depend on the use of external evocative signs" (here he cites Leont'ev and Vygotsky), and "Only when this is complete do they gradually consolidate, so that the whole process is converted into a concise action, based initially on external and then on internal speech" (p.36). In fact, we can conclude that higher mental functions's structure "does not remain constant but that they perform the same task by means of different, regularly interchanging systems of connections" (p.36).

The foundations of higher mental functions are in simple sensory processes, so disturbing these senses or their integration will cause underdevelopment. In fact, Vygotsky formulated a rule: in early stages of ontogenesis, a brain lesion will primarily affect a higher center, i.e., a function that is developmentally dependent on the area where the lesion is located. But in the stage of fully formed functional systems, a lesion in the same area will primarily affect a lower center, one regulated by that function (p.37).

We'll stop here. Luria goes on to discuss agnosia, apraxia, and various other issues associated with brain lesions as well as his diagnostic methods. But for we humble non-neurologists, the central insights of the book are in the review above. Luria clearly took Vygotsky's book on the higher mental functions as his starting point, he is unstinting with his praise for Vygotsky's work, and he used it to illuminate a new field. If you are even marginally interested in these issues, or in Soviet psychology, I highly recommend the book.

No comments: