Abstract
We developed a computer model to simulate associative memory recall of patients with chronic schizophrenia. Model inputs consisted of words derived from normative data that differed in terms of connectivity and network size, with the former quantitatively represented by parametric weights and the latter by the specific number of word associates that formed a particular network. Previous behavioral studies of normal subjects indicated better recall for words of high connectivity-small network (HCSN), followed by low connectivity-small network (LCSN), high connectivity-large network (HCLN), and low connectivity-large network (LCLN). This pattern of recall differed from that observed in behavioral studies of schizophrenic patients, which showed better recall for high connectivity words, regardless of network size. Holding constant network size while manipulating connection weights effectively simulated this schizophrenic pattern of recall. That is, manipulation of parametric weights coupled with a slight increase in noise significantly and reliably elicited the response pattern of abnormal connectivity demonstrated in the prior behavioral study of patients with chronic schizophrenia. An increase in noise was a necessary, but insufficient step in modeling the response pattern of abnormal connectivity. These findings provide support for the use of computational models to investigate dynamics of associative word recall in patients with chronic schizophrenia.
Highlights
A hallmark of the neuropsychology of schizophrenic thought disturbance is a breakdown in the associative threads that serve to interweave words, thoughts, and ideas into coherent discourse (Nestor et al, 1998)
Results of the control simulation revealed the same pattern of recall as observed for human subjects, namely high connectivity-small network (HCSN)>lLCSN>high connectivity-large network (HCLN)>low connectivity-large network (LCLN)
The findings provided support for using computer-generated, connectionist computational models to simulate associative memory performance of control subjects and patients with chronic schizophrenia
Summary
A hallmark of the neuropsychology of schizophrenic thought disturbance is a breakdown in the associative threads that serve to interweave words, thoughts, and ideas into coherent discourse (Nestor et al, 1998). Bleuler (1911/1950) first observed the intrusion of dominant but contextually inappropriate associations in schizophrenic thought as illustrated by his classic example of his patient describing her family members as “father, son, and Holy Ghost”. The locus and mechanisms that underlie schizophrenic associative disturbance have, remained elusive. It is unclear, for example, whether the schizophrenic associative disturbance reflects aberrant spread of activation within a presumed lexicon that is widely distributed across frontal and temporal lobes (Nestor et al, 1997, 1998; Caramazza, 1996). Nor has it been established as to whether the disease-related associative disturbance reflects neuronal loss or faulty modulation of preexisting synapses or connections (Nestor and O’Donnell, 1998)
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