Neural Evidence for Faster and Further Automatic Spreading Activation in Schizophrenic Thought Disorder

Abstract

It has been proposed that the loose associations characteristic of thought disorder in schizophrenia result from an abnormal increase in the automatic spread of activation through semantic memory. We tested this hypothesis by examining the time course of neural semantic priming using event-related potentials (ERPs). ERPs were recorded to target words that were directly related, indirectly related, and unrelated to their preceding primes, while thought-disordered (TD) and non-TD schizophrenia patients and healthy controls performed an implicit semantic categorization task under experimental conditions that encouraged automatic processing. By 300-400 milliseconds after target word onset, TD patients showed increased indirect semantic priming relative to non-TD patients and healthy controls, while the degree of direct semantic priming was increased in only the most severely TD patients. By 400-500 milliseconds after target word onset, both direct and indirect semantic priming were generally equivalent across the 3 groups. These findings demonstrate for the first time at a neural level that, under automatic conditions, activation across the semantic network spreads further within a shorter period of time in specific association with positive thought disorder in schizophrenia.

Examining the cognitive costs of counterfactual language comprehension: Evidence from ERPs

“…To analyze experimental effects on the N400, mean ERP amplitude was determined in two time intervals relative to target word onset: an early N400 window between 300-400ms and a late N400 window between 400-500ms. These windows were chosen based on visual inspection of the ERP waveforms and following previous studies that have employed similar experimental designs (De Grauwe et al, 2010;Kreher et al, 2008;Chwilla et al, 2000;Chwilla & Kolk, 2003;Van Petten & Kutas, 1987). ERP amplitudes were analysed using four regions of interest (ROIs).…”

Semantic Network Disconnection in Formal Thought Disorder

“…In other studies, language function in schizophrenia patients was investigated with semantic priming experiments using EEG showing strong evidence of abnormal semantic priming in schizophrenia based on event-related potentials (N400) [21,22]. Recently, using event-related potentials (N400), Kreher et al [23] and Kuperberg et al [24] found signs of increased spreading activation during semantic memory tasks to be associated with increasing severity of FTD. One of the major electrical sources of the event-related potential N400 is the left temporo-parietal junction (TPJ) [25,26], a region essential for the semantic system [27,28].…”

Association of abnormal semantic processing with delusion-like ideation in frequent cannabis users: an electrophysiological study

“…Numerous studies have found evidence for larger (more negative) than normal N400 amplitudes in response to contextually related items, and smaller than normal N400 semantic priming effects, in schizophrenia (Condray et al 2003;Condray et al 2010;Ditman and Kuperberg 2007;Kiang et al 2011;Kiang et al 2008;Kostova et al 2005;Kostova et al 2003;Laurent et al 2010;Mathalon et al 2010;Ohta et al 1999;Salisbury 2010;Salisbury 2008;Strandburg et al 1997). In contrast, a few other schizophrenia studies have found smaller than normal N400 amplitudes to contextually related targets and increased N400 relatedness priming effects (Kreher et al 2009;Kreher et al 2008;Mathalon et al 2002;Salisbury 2008). However, these latter data appear to be specific to short primetarget stimulus-onset asynchronies (SOAs; i.e., the time interval between the onsets of the two stimuli) of <300 ms, weakly related targets, and patients with disorganized speech and are thus suggestive of rapid automatic priming of weakly associated concepts in this subset of patients (Ditman and Kuperberg 2007;Kreher et al 2009;Salisbury 2008).…”