Associative memory in chronic schizophrenia: a computational model

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.

Word priming in schizophrenia: Associational and semantic influences

“…This effect in patients may be weakened, perhaps due to an associational bias that leads to restricted semantic integration and contributes to disturbed thinking. (e.g., Chapman and Chapman, 1973;Nestor et al, 1998;Han et al, 2003). However, the current findings are limited, demonstrated as statistically significant on the basis of within-but not between-group analyses.…”

Functional neuroimaging of word priming in males with chronic schizophrenia

“…These fMRI data suggested that the schizophrenic group did not process word connectivity relationships in the same manner as their demographically-matched control counterparts; showing a relatively less robust HLU regression activation pattern among language-specific left temporal and frontal regions. Given the strong empirical support for word connectivity as a parameter sensitive to the spreading of activation through lexical-semantic association networks broadly distributed across these areas (Nelson et al, 1993;Nestor et al, 1998;Han et al, 2003;Wible et al, in press), the current results suggest either a disease-related disturbance in lexical-semantic network organization, a disruption of activation through interrelated concepts, or a combination of these possibilities. Warrington (1975) presented a hierarchical model of semantic knowledge and suggested that subordinate categorical information may be more sensitive to damage than superordinate information.…”

“…Employing an empirically-derived database of word associations (Nelson et al, 1999), we were able to successfully simulate the word recall responses for both control and schizophrenic subjects. Furthermore, we were able to show evidence for an orderly degrading of network associational threads accounting for the behavioral response over and above random activation and disorganization (Han et al, 2003).…”

“…Extending this understanding to the current neurobiological correlate analysis of word connectivity processing among schizophrenia patients, Bleuler's original hypothesis of a disease-related associational breakdown is manifested either in an apparent degradation of highly associated lexical-semantic networks or "superconnectivity" of lowly associated networks such that differences between high and low connectivity networks become less salient and in effect produce a reduced discriminatory response. This coupled with a slight increase in network instability (Han et al, 2003) may serve as a foundational mechanism for specific thought disorder and speech pathology symptoms of the illness.…”

“…Nestor et al reported that schizophrenic subjects did not recall words according to connectivity as did control subjects, suggesting an abnormality in spreading activation within the schizophrenic semantic lexicon. We further investigated the implications of this study by developing a computer model to simulate the spreading activation patterns indicative of the schizophrenia illness (Han et al, 2003). Employing an empirically-derived database of word associations (Nelson et al, 1999), we were able to successfully simulate the word recall responses for both control and schizophrenic subjects.…”