Deficits in language-mediated mental operations in patients with schizophrenia

Heterogeneity of auditory verbal working memory in schizophrenia

The heterogeneity of schizophrenia remains an obstacle for understanding its pathophysiology. Studies using a tone discrimination screening test to classify patients have found evidence for 2 subgroups having either a specific deficit in verbal working memory (WM) or deficits in both verbal and nonverbal memory. This study aimed to (a) replicate in larger samples differences between these subgroups in auditory verbal WM; (b) evaluate their performance on tests of explicit memory and sustained attention; (c) determine the relation of verbal WM deficits to auditory hallucinations and other symptoms; and (d) examine medication effects. The verbal WM and tone discrimination performance did not differ between medicated (n = 45) and unmedicated (n = 38) patients. Patients with schizophrenia who passed the tone screening test (discriminators; n = 60) were compared with those who did not (nondiscriminators; n = 23) and healthy controls (n = 47). The discriminator subgroup showed poorer verbal WM than did controls and a deficit in verbal but not visual memory on the Wechsler Memory Scale-Revised (Wechsler, 1987), whereas the nondiscriminator subgroup showed overall poorer performance on both verbal and nonverbal tests and a marked deficit in sustained attention. Verbal WM deficits in discriminators were correlated with auditory hallucinations but not with negative symptoms. The results are consistent with a verbal memory deficit in a subgroup of schizophrenia having intact auditory perception, which may stem from dysfunction of language-related cortical regions, and a more generalized cognitive deficit in a subgroup having auditory perceptual and attentional dysfunction.

Current source density (CSD) old/new effects during recognition memory for words and faces in schizophrenia and in healthy adults

We previously reported a preserved 'old-new effect' (enhanced parietal positivity 300-800 ms following correctly-recognized repeated words) in schizophrenia over mid-parietal sites using 31-channel nose-referenced event-related potentials (ERP) and reference-free current source densities (CSD). However, patients showed poorer word recognition memory and reduced left lateral-parietal P3 sources. The present study investigated whether these abnormalities are specific to words. High-density ERPs (67 channels) were recorded from 57 schizophrenic (24 females) and 44 healthy (26 females) right-handed adults during parallel visual continuous recognition memory tasks using common words or unknown faces. To identify and measure neuronal generator patterns underlying ERPs, unrestricted Varimax-PCA was performed using CSD estimates (spherical spline surface Laplacian). Two late source factors peaking at 442 ms (lateral parietal maximum) and 723 ms (centroparietal maximum) accounted for most of the variance between 250 and 850 ms. Poorer (76.6+/-20.0% vs. 85.7+/-12.4% correct) and slower (824+/-170 vs. 755+/-147 ms) performance in patients was accompanied by reduced stimulus-locked parietal sources. However, both controls and patients showed mid-frontal (442 ms) and left parietal (723 ms) old/new effects in both tasks. Whereas mid-frontal old/new effects were comparable across groups and tasks, later left parietal old/new effects were markedly reduced in patients over lateral temporoparietal but not mid-parietal sites, particularly for words, implicating impaired phonological processing. In agreement with prior results, ERP correlates of recognition memory deficits in schizophrenia suggest functional impairments of lateral posterior cortex (stimulus representation) associated with conscious recollection. This deficit was more pronounced for common words despite a greater difficulty to recall unknown faces, indicating that it is not due to a generalized cognitive deficit in schizophrenia.

Neuropsychological near normality and brain structure abnormality in schizophrenia

OBJECTIVE

Cognitive deficits are prominent in schizophrenia. Patients have an average score one standard deviation below normal on a broad spectrum of cognitive tests. It has been repeatedly noted, however, that 20%-25% of patients differ from this general pattern and score close to normal on neuropsychological testing. This study used brain morphometry to 1) identify brain abnormalities associated with more severe cognitive deficits and 2) help determine whether cognitively relatively intact patients perform better because they have less severe illness or because they have a different illness.

METHOD

Patients were assigned to a neuropsychologically near normal (N=21) subgroup if they scored within 0.5 standard deviation of healthy comparison subjects (N=30) on four tests of attention and verbal and nonverbal working memory, and to a neuropsychologically impaired (N=54) group if they scored at least 1.0 standard deviation below that of comparison subjects. Subgroup assignments were confirmed with the California Verbal Learning Test and degraded-stimulus Continuous Performance Test. Volumes of ventricular compartments, hippocampus, amygdala, thalamus, cerebellum, and regional cortical gray and white matter were dependent variables. Differences among groups were evaluated by using linear mixed-model multivariate analyses with gender, age, and height as covariates.

RESULTS

Both neuropsychologically near normal and neuropsychologically impaired patients had markedly smaller gray matter and larger third ventricle volumes than healthy comparison subjects. Only neuropsychologically impaired patients, however, had significantly smaller white matter and larger lateral ventricle volumes than healthy comparison subjects.

CONCLUSIONS

Although both neuropsychologically impaired and neuropsychologically near normal patients have marked neuropathology in their gray matter, the relative absence of white matter pathology in the neuropsychologically near normal group suggests the possibility of differences in the disease process.

The cognitive neuroscience of working memory: relevance to CNTRICS and schizophrenia

Working memory is one of the central constructs in cognitive science and has received enormous attention in the theoretical and empirical literature. Similarly, working memory deficits have long been thought to be among the core cognitive deficits in schizophrenia, making it a ripe area for translation. This article provides a brief overview of the current theories and data on the psychological and neural mechanisms involved in working memory, which is a summary of the presentation and discussion on working memory that occurred at the first Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS) meeting (Washington, D.C.). At this meeting, the consensus was that the constructs of goal maintenance and interference control were the most ready to be pursued as part of a translational cognitive neuroscience effort at future CNTRICS meetings. The constructs of long-term memory reactivation, capacity, and strategic encoding were felt to be of great clinical interest but requiring more basic research. In addition, the group felt that the constructs of maintenance over time and updating in working memory had growing construct validity at the psychological and neural levels but required more research in schizophrenia before these should be considered as targets for a clinical trials setting.

The cognitive neuroscience of schizophrenia

Individuals with schizophrenia experience a range of cognitive deficits and associated dysfunctions in the neural systems that support cognitive processes. This chapter reviews the literature on disturbances in working memory, executive control, and episodic memory in schizophrenia. Advances in basic cognitive neuroscience are described to help explain the cognitive neuroscience of schizophrenia. For working memory in schizophrenia, evidence is reviewed regarding deficits in the verbal (phonological loop) and nonverbal (visual-spatial scratch pad) buffer systems as well as in the central executive function. In the domain of episodic memory, evidence is reviewed for deficits in recollection versus familiarity processes in episodic memory. Also discussed are conceptual issues and potential confounds relevant to understanding the cognitive neuroscience of schizophrenia, including the role that cognitive deficits play in the developmental course of schizophrenia, relationships to specific symptom domains, behavioral performance confounds, and medication influences on behavioral performance and brain function.

ERP/CSD indices of impaired verbal working memory subprocesses in schizophrenia

To disentangle subprocesses of verbal working memory deficits in schizophrenia, long EEG epochs (>10 s) were recorded from 13 patients and 17 healthy adults during a visual word serial position test. ERP generator patterns were summarized by temporal PCA from reference-free current source density (CSD) waveforms to sharpen 31-channel topographies. Patients showed poorer performance and reduced left inferior parietotemporal P3 source. Build-up of mid-frontal negative slow wave (SW) in controls during item encoding, integration, and active maintenance was absent in patients, whereas a sustained mid-frontal SW sink during the retention interval was comparable across groups. Mid-frontal SW sinks (encoding and retention periods) and posterior SW sinks and sources (encoding only) were related to performance in controls only. Data suggest disturbed processes in a frontal-parietotemporal network in schizophrenia, affecting encoding and early item storage.

What can research on schizophrenia tell us about the cognitive neuroscience of working memory?

Work with individuals with lesions to specific brain regions has long been used to test or even generate theories regarding the neural systems that support specific cognitive processes. Work with individuals who have neuropsychiatric disorders that also involve neurobiological disturbances may be able to play a similar role in theory testing and building. For example, schizophrenia is a psychiatric disorder thought to involve a range of neurobiological disturbances. Further, individuals with schizophrenia are known to suffer from deficits in working memory, meaning that examining the work on the neurobiology of working memory deficits in schizophrenia may help to further our understanding of the cognitive neuroscience of working memory. This article discusses the pros and cons of extrapolating from work in schizophrenia to models of healthy working memory function, and reviews the literature on working memory function in schizophrenia in relationship to existing human and non-human primate models of the cognitive neuroscience of working memory.

Verbal memory deficit in patients with schizophrenia: an important future target for treatment

Despite more than two-thirds of patients with schizophrenia showing reductions in delusions and hallucinations following optimum available treatment, many are left with crippling cognitive impairments. Neurocognitive deficit is a core feature of schizophrenia, but the question arises as to whether efforts should be geared towards ameliorating and normalizing these deficits. Verbal memory dysfunction is one of the most consistently reported cognitive deficits and among the best predictors of functional outcome in schizophrenia. Therefore, a better understanding of the nature of this deficit could lead to treatments that not only improve the specific systems mediating the impairment, but could also have wider implications for clinical and social outcome.

Processing of environmental sounds in schizophrenic patients: disordered recognition and lack of semantic specificity

The recognition of environmental sounds is an important feature of higher auditory processing and essential for everyday life. The present study aimed to investigate the potential impairment of this mental function in schizophrenia. This work on immediate sound recognition is complementary to recent studies on auditory linguistic processing. Fifteen schizophrenic patients and 30 control subjects were asked to identify 43 complex environmental sounds from different categories and rate their familiarity when naïve to the sounds. In consecutive experiments, patients and control subjects rated the sounds according to emotional valence and arousal, as well as imageability. In both groups, correct identification of non-verbal sounds was highly associated with familiarity. Statistical analysis by group demonstrated a significantly higher error rate in identifying sounds in patients suffering from schizophrenia compared to healthy control subjects. In contrast, the affective recognition of the complex sounds was preserved in the schizophrenic patients. These results suggest a disturbance of higher-order, auditory mnemonic processing in schizophrenic patients in the non-linguistic domain. We discuss their abnormal responses in the context of recent theories of auditory physiological and semantic processing deficits in schizophrenia.

Ear of stimulation determines schizophrenia-normal brain activity differences in an auditory paired-stimuli paradigm

Schizophrenia patients have abnormalities of auditory information processing, theoretically associated with dysfunction of neuronal excitation. Auditory paired-stimuli (S1-S2) paradigms are used to evaluate the nature of these abnormalities. It is unknown whether patients' abnormalities during S1-S2 paradigms are attributable to specific hemispheric differences in cortical processing. The present studies used whole head magnetoencephalography and monaural or binaural versions of the paired-stimuli paradigm to evaluate auditory processing among 38 schizophrenia and 38 normal subjects. The strengths of auditory-evoked brain responses over time were quantified using distributed source reconstructions with L2 minimum norm constraint and realistic head models. For left ear stimuli, schizophrenia and normal groups did not differ on either left or right hemisphere activity over auditory cortex. For right ear and binaural stimuli, schizophrenia patients had less activity over left auditory cortex from 80 to 120 ms post-stimulus but did not differ from normal on activity over right auditory cortex. Additionally, in response to monaural stimulation, schizophrenia patients had significantly less activity than normal over right temporal parietal junction from 60 to 120 ms post-stimulus. These data are consistent with four propositions about schizophrenia: (i). right auditory cortex is functioning normally; (ii). processing of simple auditory stimuli is abnormal in left auditory cortex, probably specifically in supra-granular layers; (iii). auditory localization abilities are deficient; and (iv). auditory cortex abnormalities are not a function of deficient hemispheric communication because they are evident early in processing as long as stimuli are delivered directly to left hemisphere.