Mental retardation consciousness

This chapter is concerned with the neurochemical basis of developmental disability which is considered here in two forms the globally delayed or halted development seen in mental retardation, and the more circumscribed pattern of disordered development of autism. A range of deficits of important key aspects of consciousness are apparent in both conditions. Of particular relevance to consciousness are the cognitive and behavioural impairments in attention, concentration, memory, information processing and social behaviour which are commonly present. Consideration of aberrant neurotransmitter activities in these developmental deficits may provide insights into the role of neurotransmitters in consciousness. 

This diversity of mental retardation, in both cause and phenotype, carries important implications for consideration of the biochemistry of consciousness. On the one hand, because this is an investigation of multiple causalities—including, for example, inborn errors of metabolism, each of which has its own unique biochemical profile (Cook Leventhal, 1996), it may not prove possible to identify specific neurotransmitter abnormalities which are common to mental retardation as such. On the other hand common themes concerning key neurotransmitters may be identified from studies of mental retardation. Altered neurotransmitter functioning associated with the severity of mental retardation is open to different interpretations, either reflecting fundamentally impaired development of cerebral structure or a more general impairment of central transmitter activity and functioning. 

Dopamine plays a key role in the regulation of cognition (Chapters 10 and 17) and control of movement. Given the abnormalities in these domains in mental retardation, any association between dopamine and mental retardation may be relevant to the neurochemistry of consciousness, especially relating to cognition. 

If there is an association between the extent or severity of abnormal neurotransmitter functioning and the global measure of severity of autism, the direction and mechanism of causality may still be unclear (as has been discussed in mental retardation). However, neurotransmitter correlates of specific aspects of autism, such as social isolation or obsessional behaviour, are likely to be more revealing and of greater relevance to the study of consciousness. 

Psychiatric disorders must be considered to have a biochemical basis. Psychosis, neurosis, mental retardation, and behavior problems must, in the last analysis, be complex manifestations of some aberration of biochemical functioning of the central nervous system. Fig. 3 diagrams how one may conceptualize mental function in terms of intermediary metabolism. Mental function can be expressed in terms of an individual s intelligence, personality, and patterns of behavior. These outward manifestations of mental function can be considered to be complex expressions of consciousness (self-awareness), sensory perception (awareness of reality of the outside world), volition (decision making), memory, learning, creative ability (problem solving), and emotional reactivity (which is partially subconscious). All of these components are some function of the nerve network. How the nerve network gives rise to these components is unknown. It is apparent from... 

---