The concept of locally specialized functions dominates research on higher brain function and its disorders. Locally specialized functions must be complemented by processes that coordinate those functions, however, and impairment of coordinating processes may be central to some psychotic conditions. Evidence for processes that coordinate activity is provided by neurobiological and psychological studies of contextual disambiguation and dynamic grouping. Mechanisms by which this important class of cognitive functions could be achieved include those long-range connections within and between cortical regions that activate synaptic channels via NMDA-receptors, and which control gain through their voltage-dependent mode of operation. An impairment of these mechanisms is central to PCP-psychosis, and the cognitive capabilities that they could provide are impaired in some forms of schizophrenia. We conclude that impaired cognitive coordination due to reduced ion flow through NMDA-channels is involved in schizophrenia, and we suggest that it may also be involved in other disorders. This perspective suggests several ways in which further research could enhance our understanding of cognitive coordination, its neural basis, and its relevance to psychopathology.

I report a series of single case studies involving an aphasic patient, H.G., which illustrates both the usefulness and the limitations of cognitive neuropsychological models and methods in aphasia rehabilitation. The first set of experiments analyze H.G.'s pattern of performance across lexical tasks in order to identify the loci of her damage to the cognitive mechanisms underlying the tasks of naming, comprehension, repetition, reading, and spelling. The second set of studies evaluates her response to two different types of treatment and identifies a few of the variables that influence the effectiveness of treatment. (JINS, 1998, 4, 648–660.)