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The richness of this subject has become apparent with the development of tests assessing an increasing array of aspects of cognitive function. This, coupled with intelligent use of structural and to an increasing extent functional, brain imaging, encourages the development of developmental brain/behaviour modules as never before.
It is timely then to have a book which reviews progress in the area—even if only to show the gaps in our understanding and the vast amount of work remaining to be done.
Arthur Benton, the doyen of localisation, provides an interesting historical perspective in an introductory chapter.
There follows one of four chapters by his coeditor Daria Riva, the first on memory and temporomesial structures. The clinical literature is usefully presented; general conclusions are offered as fact rather than as the hypotheses they are—although none the less interesting for that—namely, that the cerebral cortex stores information which is then codified in parahippocampal structures. The function of the hippocampus is to analyse the components of experience and to construct relations between different aspects of experience in flexible and potentially infinite ways, thereby creating a uniquely personal mental map.
Then follow three essays on lateralisation of hemisphere function as derived from studies of callosal deficits—congenital and acquired. The picture which tends to emerge from congenital agenesis of the corpus callosum is one of duplication of function in the separate hemispheres, with a general impoverishment of function. The extent to which this (or lateralisation) occurs may depend on maximal use of subcortical commissures and ipsilateral projections. That tests requiring interhemispheric transmission of visuomotor information take longer in children with agenesis, but shorter than in callosotomy patients may be explained by a better ability to use such compensatory pathways during development than in later life.
Three essays address the issue of language development, the hope being that children with early acquired brain lesions will shed light. Initial studies selected children with hemiplegia creating the myth that children had non-fluent aphasias only. Paquier and Van Dongen analysed the sparse literature on fluent aphasia in children and point out that this arises in conjunction with posterior lesions in 25 of 33 cases. Conversely, in the majority with non-fluent aphasias lesions are in prerolandic or perirolandic structures. A similar echo of adult organisation is found in the analysis of the 16 reported cases of subcortical aphasia by Martins. Lesions in anterior subcortical structures tend to produce non-fluent aphasias with preserved comprehension, whereas lesions in posterior structures lead to fluent aphasias with impaired comprehension perhaps by interrupting auditory pathways in the temporal isthmus. Unless both anterior and posterior structures are involved recovery is better than in adults. Also, unlike adults, major behavioural problems are rare.
The pattern begins to differ radically from adult aphasiology if the effect of lesions acquired prelingually—either prenatally or perinatally—are studied. The position, summarised by Reilly, is that both right and left hemisphere-damaged children initially show delay in comprehension and speech and show more grammatical errors of the kind shown by younger undamaged children. However by 7-10 years their language function is within the normal range. This suggests that brain areas required to develop language are more broadly distributed than those used to maintain language, that normality by 7-10 suggests a degree of plasticity, and that acquisition of language has fairly rigid processes with developmental deficits being those of timing rather than of kind.
Byron Rourke tries to summarise 29 years' work on right hemisphere non-verbal learning disabilities in seven pages. The picture which emerges is one of deficits in visiospatial function, tactile, perceptual and coordination difficulties particularly on the left, and furthermore a behavioural stereotype with difficulty in dealing with new solutions, difficulty in using feedback in complex situations, poor time concept, poor language pragmatics, phonetic misspellings, poor prosody and poor social skills, with conversely a good rote memory and a tendency to repetitive verbosity (this must bring to mind someone you know!). Lack of space in his account is compensated for by plenty of references.
There is a rehearsal of agnosias as defined by the adult neurology literature by Nichelli and Riva. They found no well documented accounts of agnosias in childhood and only two cases of non-lesional and presumed developmental prosop agnosia. An opportunity for someone.
Head injuries causing prefrontal damage are dealt with by Levin and Chapman. They document the damage to executive function and correlates with the degree of recovery from age 7-13. Dorsolateral prefrontal injury in infant monkeys only manifests in the adult. They are following up their children to see if a similar phenomenon occurs in humans.
Finally, arguments for the influence of the cerebellum on the cognitive development is summarised. Riva again contributes his clinical experience suggesting that after left cerebellar astrocytoma resection there is impairment of right hemisphere skills, whereas conversely after right cerebellar resection there is deterioration of left hemisphere skills.
It makes me uneasy that several of the authors present their own clinical experience, which in this format is non-peer reviewed. Indeed, published here it may not be presented elsewhere which also makes for access difficulties if your own library happens not to take this book. This rather begs the question of the function of collections such as these. Perhaps the Mariani Foundation should consider putting out future publications in their entirety on the Internet.
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