Semantic disturbance in schizophrenia and its relationship to the cognitive neuroscience of attention

Abstract

We view schizophrenia as producing a failure of attentional modulation that leads to a breakdown in the selective enhancement or inhibition of semantic/lexical representations whose biological substrata are widely distributed across left (dominant) temporal and frontal lobes. Supporting behavioral evidence includes word recall studies that have pointed to a disturbance in connectivity (associative strength) but not network size (number of associates) in patients with schizophrenia. Paralleling these findings are recent neural network simulation studies of the abnormal connectivity effect in schizophrenia through 'lesioning' network connection weights while holding constant network size. Supporting evidence at the level of biology are in vitro studies examining N-methyl-D-aspartate (NMDA) receptor antagonists on recurrent inhibition; simulations in neural populations with realistically modeled biophysical properties show NMDA antagonists produce a schizophrenialike disturbance in pattern association. We propose a similar failure of NMDA-mediated recurrent inhibition as a candidate biological substrate for attention and semantic anomalies of schizophrenia.

Associative memory in chronic schizophrenia: a computational model

“…Indeed, the rationale for the manipulation came from prior behavioral studies of patients with chronic schizophrenia that have pointed to a diseaserelated disturbance in information processing characterized by over-responding of dominant associates, regardless of context, at the expense of weaker associates. The simulation results thus concurred with prior theoretical interpretations that have suggested overactivation of dominant associates and underactivation of weak associations in the schizophrenic lexicon (Chapman et al, 1964;Nestor et al, 2001), as well as aberrant activation and network instability across a variety of methodologies (Nestor et al, 1993Shenton et al, 1992;Niznikiewicz et al, 1997).…”

“…Although other manipulations and certainly other models are likely to be developed to simulate associative memory in schizophrenia, the current findings pointed to the relative specificity of the simulation that targeted association weight modulation in modeling schizophrenic associative memory performance. These findings may very well be viewed as additional evidence of the importance of associative links that bind words within a lexicon widely distributed across frontal and temporal lobes to the neuropsychological disturbance of schizophrenia (Nestor et al, 2001).…”

“…Detailed elements of the model are also described in Nestor et al (2001), and a full description of the model, including complete syntax and readme file printout, is given in .…”

The role of retrieval inhibition in the associative memory impairment of schizophrenia

“…The associative disturbance of schizophrenia is often characterized by difficulties overriding prepotent, dominant responses, as illustrated in the foregoing Bleuler example (see Han et al, 2003;Nestor et al, 1998;Nestor et al, 2002) We therefore manipulated associative strength word pair exemplars taken from strong and weak categories to examine the effect of categorical dominance on RIF for both recall and recognition in patients with chronic schizophrenia.…”

Can disorganisation of semantic memory account for the abnormalities of thought in schizophrenia?a controlled experimental study

“…Process theories of disorganised semantic memory in schizophrenia have included impaired selective attention (Nestor et al 2001), or dysexecutive theories (e.g. Allen et al 1994, Ragland et al 2001.…”