Neuropsychology of schizophrenia: The “hole” thing is wrong

Integrative circuit models and their implications for the pathophysiologies and treatments of the schizophrenias

A preponderance of evidence indicates that the heterogeneous group of schizophrenias is accompanied by disturbances in neural elements distributed throughout multiple levels of interconnected cortico-striato-pallido-thalamic circuitry. These disturbances include a substantial loss of, or failure to develop, both cells and/or appropriate cellular connections in regions that include at least portions of the hippocampus, parahippocampal gyrus, entorhinal cortex, amygdala, prefrontal and anterior cingulate cortex, superior and transverse temporal gyri, and mediodorsal, anterior, and pulvinar nuclei of the thalamus; they appear to reflect failures of early brain maturation, that become codified into dysfunctional circuit properties, that in the opinion of this author cannot be "undone" or even predictably remediated in any physiological manner by existing pharmacotherapies. These circuit disturbances are variable across individuals with schizophrenia, perhaps reflecting the interaction of multiple different risk genes and multiple different epigenetic events. Evidence for these complex circuit disturbances has significant implications for many areas of schizophrenia research, and for future efforts toward developing more effective therapeutic approaches for this group of disorders. The conclusion of this chapter is that such future efforts should focus on further developing and refining medications that target nodal or convergent circuit points within the limbic-motor interface, with the goal of constraining the scope and severity of psychotic exacerbations, to be used in concert with systematic rehabilitative psychotherapies designed to engage healthy neural systems to compensate for and replace dysfunctional higher circuit elements. This strategy should be applied in both preventative and treatment settings, and disseminated for community delivery via an evidence-based manualized format. In contrast to alternative treatment strategies that range from complex polypharmacy to gene therapies to psychosurgical interventions, the use of combined medication plus targeted cognitive and behavioral psychotherapy has both common sense and time-tested documented efficacy with numerous other neuropsychiatric disorders.

Obsessive-compulsive disorder and tic syndromes

The phenomenology of OCD and TS seem to match perfectly with the existing conceptualization of the functional relationship between frontal cortical and subcortical circuits. Failed editing of thoughts and impulses, perseverative patterns, and inhibitory deficits are the most convenient descriptors of the symptoms, and some operationalized measures can capture evidence for such deficits in TS and OCD patients. Beyond these expectations borne from conceptual models and some broad patterns of distributed metabolic disturbances in neuroimaging studies, a specific causal pathology within CSPT circuitry needs to be identified in these disorders. This is not a criticism of the existing studies of TS and OCD; to the contrary, the scarcity of pathologic material, the limits of resolution of existing technologies, and the heterogeneity of the phenotypes make the accomplishments of these studies more impressive. As clinicians strive to integrate clinical and scientific findings into coherent models for the pathophysiology of OCD and TS, it is useful to identify practical and effective strategies for therapeutic interventions.

Distributed neurodegenerative changes 2-28 days after ventral hippocampal excitotoxic lesions in rats

An enhanced sensitivity to the behavioral effects of dopamine (DA) agonists in adult rats occurs after cytotoxic lesions of the ventral hippocampus (vHPC). While some of these behavioral changes may model specific abnormalities in schizophrenia patients, little is known about the cellular events that underlie vHPC lesion-induced behavioral DA 'supersensitivity'. Neuropathological consequences of excitotoxin lesions of the vHPC were investigated in this study. Adult male rats received vehicle or ibotenic acid infusions into the vHPC, using parameters that produce an enhanced sensitivity to the prepulse inhibition-disruptive effects of the DA agonist apomorphine, 1 month post-lesion. A total of 27 rats were sacrificed, 2, 7, 14, 21 or 28 days post-lesion. Amino-cupric-silver staining demonstrated degenerative changes throughout the hippocampus, and in hippocampal efferent projections to forebrain structures, including the septal nucleus and nucleus accumbens (NAC), and within the olfactory tubercle (OT) and orbital cortex. Silver-impregnated fibers were identified in the substantia nigra reticulata (SNr), NAC, OT, septum and orbital cortex. Some degenerative changes were noted at the earliest time point (2 days post-lesion), while others were delayed in appearance. Adjacent sections stained for tyrosine hydroxylase (TH) immunocytochemistry revealed reduced TH labeling through forebrain DA terminal fields 28 days, but not 14 days after VH lesions. Excitotoxic lesions of the vHPC result in distributed neurotoxic changes in subcortical and cortical brain regions; these changes may contribute to the delayed emergence of DA-mediated behavioral abnormalities in these animals.

Schizophrenia, psychosis, and the basal ganglia

Schizophrenia is one of the most common and perhaps the most disabling of mental disorders, for which effective forms of treatment have not yet been established definitively. The findings reviewed in this article strongly suggest that basal ganglia abnormalities are involved in the pathophysiology of psychotic syndromes in general, and schizophrenia in particular.

Hippocampal modulation of acoustic startle and prepulse inhibition in the rat

Prepulse inhibition (PPI) is the normal reduction in a startle response that occurs when the startling stimulus is preceded by a weak lead stimulus ("prepulse"). Schizophrenic patients exhibit abnormally low levels of PPI; therefore, animal models of deficient PPI may provide information regarding neural dysfunctions underlying schizophrenia. We recently reported that infusion of the cholinergic agonist carbachol into the dentate gyrus (DG) disrupts PPI in the rat. We now report the effects of carbachol microinjected into CA1, the DG, or the ventral subiculum (VS) on acoustic startle and PPI. Carbachol infusion into CA1 or the DG depressed startle. Carbachol infusion decreased PPI with a regional rank-order potency CA1 > DG > VS. CA1 infusions more potently depressed the startle reflex. By contrast, DG infusions preferentially decreased PPI, while VS infusions decreased PPI without altering startle amplitude. Coinfusion with the muscarinic cholinergic antagonist atropine opposed the effects of carbachol. These results demonstrate the regional heterogeneity and pharmacological specificity of the hippocampal cholinergic modulation of acoustic startle and PPI and suggest that abnormalities within various regions of the hippocampal formation may contribute to deficient sensorimotor gating in schizophrenic patients.