Genetic and environmental influences on the organisation of semantic memory in the brain:is "living things" an innate category?

The organisation of semantic memory into separately lesionable or imageable components must be determined by some combination of genetic and environmental factors. Little is known about the relative contributions of these two factors in establishing the functional architecture of semantic memory. By assessing the semantic memory impairment of an individual who sustained brain damage as a newborn, it is possible to place an upper bound on the contribution of post-natal experience. The present case study demonstrates a profound and enduring impairment in knowledge of "living things" following posterior cerebral artery infarctions at approximately 1 day of age. The design of the two experiments reported here allows us to characterise the subject's semantic memory impairment in terms of its scope and selectivity. The impairment affects both the naming of pictures of living things and the retrieval of verbal information about living things. It cannot be accounted for by differences in the difficulty of retrieving knowledge of living and nonliving things, as the living and nonliving items were equated for difficulty in each experiment. When visual and nonvisual information were queried separately for living and nonliving things, the impairment was manifest for both kinds of information about living things, but for neither kind of information about nonliving things. Because this impairment resulted from brain damage sustained too early for experience to have contributed to the organisation of semantic memory, this case study supports a genetic basis for the living-nonliving distinction in semantic memory.