Dopamine, schizophrenia, mania, and depression: Toward a unified hypothesis of cortico-striatopallido-thalamic function

Influence of the entorhinal cortex on accumbal and striatal dopaminergic responses in a latent inhibition paradigm

The use of latent inhibition paradigms is one means of investigating the involvement of mesencephalic dopaminergic (DA) neurons in cognitive processes. We have shown recently that DA neurons reaching the core and the dorsomedial shell parts of the nucleus accumbens and the anterior part of the striatum are differentially involved in latent inhibition. In other respects, theoretical, behavioral and anatomo-functional data suggest that the entorhinal cortex (ENT) may control latent inhibition expression. In this study, using in vivo voltammetry in freely moving rats, we investigated the influence of the ENT on the DA responses obtained in the core and dorsomedial shell parts of the nucleus accumbens and the anterior part of the striatum. For this purpose a reversible inactivation of the left ENT was achieved by the local microinjection of tetrodotoxin, 3 h before pre-exposure to the conditional stimulus (banana odour). During the second session, animals were aversively conditioned to banana odour. Results obtained during the third session (test session), in animals submitted to the reversible blockade of the ENT before the first session were as follows: (1) pre-exposed conditioned animals displayed behavioral aversive responses; (2) where core DA responses were concerned, responses were situated between those observed in pre-exposed and non-pre-exposed conditioned animals; (3) by contrast, where the dorsomedial shell part of the nucleus accumbens and the anterior striatum were concerned, DA variations were not statistically different in pre-exposed and non-pre-exposed conditioned rats. These data suggest that the left ENT exerts a crucial influence over the latent-inhibition-related DA responses in the left dorsomedial shell part of the nucleus accumbens and the left anterior part of the striatum, whereas one or more other brain regions control DA variations in the left core part of the nucleus accumbens. These data may help us to understand the pathophysiology of schizophrenic psychoses.

Glutamate and Depression

The past decade has seen a steady accumulation of evidence supporting a role for the excitatory amino acid (EAA) neurotransmitter, glutamate, and its receptors in depression and antidepressant activity. To date, evidence has emerged indicating that N-methyl-d-aspartate (NMDA) receptor antagonists, group I metabotropic glutamate receptor (mGluR1 and mGluR5) antagonists, as well as positive modulators of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors have antidepressant-like activity in a variety of preclinical models. Moreover, antidepressant-like activity can be produced not only by drugs modulating the glutamatergic synapse, but also by agents that affect subcellular signaling systems linked to EAA receptors (e.g., nitric oxide synthase). In view of the extensive colocalization of EAA and monoamine markers in nuclei such as the locus coeruleus and dorsal raphe, it is likely that an intimate relationship exists between regulation of monoaminergic and EAA neurotransmission and antidepressant effects. Further, there is also evidence implicating disturbances in glutamate metabolism, NMDA, and mGluR1,5 receptors in depression and suicidality. Finally, recent data indicate that a single intravenous dose of an NMDA receptor antagonist is sufficient to produce sustained relief from depressive symptoms. Taken together with the proposed role of neurotrophic factors in the neuroplastic responses to stressors and antidepressant treatments, these findings represent exciting and novel avenues to both understand depressive symptomatology and develop more effective antidepressants.

Dopamine receptor-interacting proteins: the Ca(2+) connection in dopamine signaling

Abnormal activity of the dopamine system has been implicated in several psychiatric and neurological illnesses; however, lack of knowledge about the precise sites of dopamine dysfunction has compromised our ability to improve the efficacy and safety of dopamine-related drugs used in treatment modalities. Recent work suggests that dopamine transmission is regulated via the concerted efforts of a cohort of cytoskeletal, adaptor and signaling proteins called dopamine receptor-interacting proteins (DRIPs). The discovery that two DRIPs, calcyon and neuronal Ca(2+) sensor 1 (NCS-1), are upregulated in schizophrenia highlights the possibility that altered protein interactions and defects in Ca(2+) homeostasis might contribute to abnormalities in the brain dopamine system in neuropsychiatric diseases.

Differential involvement of dopamine in the anterior and posterior parts of the dorsal striatum in latent inhibition

The involvement of mesostriatal dopaminergic neurons in cognitive operations is not well understood, and needs to be further clarified. The use of latent inhibition paradigms is a means of investigating cognitive processes. In this study, we investigated the involvement in latent inhibition of dopaminergic inputs in the anterior part and posterior part of the dorsal striatum. The latent inhibition phenomenon was observed in a conditioned olfactory aversion paradigm. Changes in extracellular dopamine levels induced by the conditioned olfactory stimulus (banana odor) were monitored in the two parts of the dorsal striatum in the left hemisphere after pre-exposure to the olfactory stimulus using in vivo voltammetry in freely moving rats. During the conditioning session animals received either an i.p. injection of NaCl (0.9%) (control groups) or an i.p. injection of LiCl (0.15 M) (conditioned groups). Dopamine variations and place preference or aversion toward the stimulus were analyzed simultaneously in pre-exposed and non-pre-exposed animals. Data collected during the retention (test) session were as follows. Where the anterior part of the striatum was concerned, similar enhancements in dopamine levels (+100%) were obtained in pre-exposed and non-pre-exposed control animals, as well as in the pre-exposed experimental animals. In contrast, dopamine levels in the non-pre-exposed experimental group (conditioned animals) remained fairly consistently close to the baseline after the presentation of the olfactory stimulus. Where the posterior part of the striatum was concerned, increases in extracellular dopamine levels were similar (+50%) for the different groups. The present results suggested that dopaminergic neurons reaching the anterior part of the dorsal striatum are implicated in the latent inhibition phenomenon and affective perception, whereas dopaminergic terminals in the posterior part of the dorsal striatum appeared to be involved neither in latent inhibition nor in affective perception of the stimulus, seeming only to be affected by the intrinsic properties of the stimulus. Cognitive as well as affective deficits have been reported in patients with schizophrenia. Thus the present data may be considered in the context of the pathophysiology of schizophrenic psychoses.

Basal ganglia systems in ritualistic social displays: reptiles and humans; function and illness

Complex, situation-specific territorial maintenance routines are similar across living terrestrial vertebrates (=amniotes). Decades ago, Paul MacLean et al., at the Laboratory of Brain Evolution and Behavior of the National Institute of Mental Health, postulated that these are evolutionarily conserved behaviors whose expression is mediated by the similarly conserved amniote basal ganglia and related brain systems (BG systems). Therefore, they undertook studies in nonhuman primates and in small social lizards (the common green anole, Anolis carolinensis) to examine this idea. MacLean et al. also postulated that when BG systems misfunction in humans, behavioral abnormalities result, some of them under the rubric of psychiatric illnesses. Obsessive-compulsive disorder (OCD) was singled out as one likely candidate. In the last dozen years, functional brain imaging studies of OCD patients have validated the contention that this is, in fact, a condition involving dysfunctioning BG systems. Inspired by the MacLean group's original investigations, my colleagues and I have now applied related functional imaging techniques in naturalistic experiments using Anolis to better understand BG systems' roles in the mediation of complex behavioral routines in healthy amniotes. Here, I will review this functional imaging work in primates (man, and a little in monkey) and in lizards. I believe the literature not only supports MacLean et al.'s contentions about BG systems and behavior in general, but also validates Paul MacLean's life-long contention that human behavioral medicine can profit from a broad comparative approach.

Neuroimaging studies of mood disorder effects on the brain

Studies of early-onset recurrent depression, late life depression associated with neurologic disorders, and bipolar illness have revealed structural brain changes within a neuroanatomical circuit. This circuit, originally described by, has been termed the limbic-cortical-striatal-pallidal-thalamic tract and is comprised of structures which are extensively interconnected. In three-dimensional magnetic resonance imaging studies of affective illness, many of the structures that comprise this tract have been found to have volume loss or structural abnormalities. Mechanisms proposed to explain volume loss in depression include glucocorticoid neurotoxicity, decreased brain-derived growth factor, decreased neurogenesis, and loss of plasticity.

An fMRI study of affective state and medication on cortical and subcortical brain regions during motor performance in bipolar disorder

Structural neuroimaging studies have identified abnormalities in the basal ganglia in patients with bipolar disorder. Findings have been mixed with regard to affective state and have not elaborated on the role of medication on functional brain activity. The aims of the present study were to use functional magnetic resonance imaging (fMRI) to test whether depressed and manic bipolar disorder patients differ in terms of activity in cortical and subcortical brain areas and to examine the effects of psychotropic medication. Twenty-four bipolar disorder subjects and 13 healthy comparison subjects participated in an fMRI study of manual reaction time. Both manic and depressed subjects exhibited abnormally elevated blood oxygen level dependent BOLD responses in cortical and subcortical areas. Manic bipolar subjects had significantly higher BOLD responses in the left globus pallidus and significantly lower BOLD responses in the right globus pallidus compared with depressed bipolar patients. Correlational analyses revealed significant relationships between the severity of mania and activity within the globus pallidus and caudate. Patients off antipsychotic or mood-stabilizing medication exhibited significantly higher BOLD responses throughout the motor cortex, basal ganglia and thalamus compared with patients on these medications. These results suggest that affective state in bipolar disorder may be related to a disturbance of inhibitory regulation within the basal ganglia and that antipsychotics and/or mood stabilizers normalize cortical and subcortical hyperactivity.

The legacy of the silver methods and the new anatomy of the basal forebrain: implications for neuropsychiatry and drug abuse

The first part of the paper highlights the remarkable legacy of the silver methods, with special emphasis on the travails and opportunities offered by the various Nauta methods and their modifications. When the tracer methods based on axoplasmic flow were introduced in the early 1970s, they were exploited on a backdrop of a basic anatomical framework, which had already been established through the tracing of the major CNS pathways by the aid of the silver methods, especially the widely used Nauta-Gygax methods and their modifications. Some of the silver methods that were developed in the late 1960s for the staining of degenerating boutons (e.g. the Fink-Heimer method and de Olmos cupric silver method) provided the necessary technical improvements that eventually led to a new and more productive way to look at the basal forebrain functional/anatomical organization; if it was not for the silver methods, we would in all likelihood still be promoting the nebulous notion of the substantia innominata rather than the concepts of the ventral striatopallidal system and the extended amygdala. The discovery and elaboration of these two macroanatomical systems symbolize what might deservedly be called the "new anatomy" of the basal forebrain. Following a review of the critical experiments which led to the development of the new anatomy of the basal forebrain, its topography in the human is reviewed in drawings of an abbreviated series of coronal sections. The discovery of the ventral striatopallidal system and its thalamic projection to the mediodorsal thalamus rather than to the ventral anterior-ventral lateral thalamic complex ushered in the idea of parallel cortico-subcortical reentrant circuits, which to a large extent has replaced the limbic system as a theoretical framework for neuropsychiatric disorders. The extended amygdala, which appears as a large ring formation around the internal capsule, is still controversial in some quarters, although it is slowly but surely making its way into the general neuroscience literature, especially in the field of addictive disorders. The ventral striatopallidal system and the extended amygdala are interwoven in a complex fashion with the basal nucleus of Meynert within the basal forebrain. Together, these three systems represent important output channels for so-called "limbic" forebrain regions, especially orbitomedial prefrontal cortex and medial temporal lobe structures, which are increasingly implicated in major neuropsychiatric disorders.

Heritable differences in the effects of amphetamine but not DOI on startle gating in albino and hooded outbred rat strains

Sensorimotor gating, measured by prepulse inhibition (PPI) of the startle reflex, is reduced in schizophrenia patients and in rats treated with dopamine (DA) agonists. Strain and substrain differences in the sensitivity to the PPI-disruptive effects of DA agonists may provide insight into the basis for human population differences in sensorimotor gating. We reported heritable differences in sensitivity to the PPI-disruptive effects of the D1/D2 agonist apomorphine (APO) in Harlan Sprague-Dawley (SDH) and Long-Evans (LEH) rats, offspring (F1) of an SDHxLEH cross, and subsequent offspring (N2) of an SDHxF1 cross. In this study, we assessed the neurochemical specificity of this heritable phenotype across parental SDH and LEH strains, and their F1 and N2 offspring, based on their sensitivity to the PPI-disruptive effects of the indirect DA agonist D-amphetamine (AMPH) and the 5HT2A agonist DOI. AMPH sensitivity followed a gradient of SDH>N2>F1>LEH, consistent with past findings with APO. DOI sensitivity did not differ across strains or generations. These findings demonstrate that the heritable phenotype in this model is not specific to a particular compound (APO), and reflects physiological differences in the DAergic, but not serotonergic, regulation of PPI.

Neuroimaging and neurocircuitry models pertaining to the neurosurgical treatment of psychiatric disorders

Neurocircuitry models of obsessive-compulsive disorder (OCD) and major depression (MD) are described, focusing on relevant supporting neuroimaging data. Corticostriatothalamocortical circuitry is implicated in OCD. In MD, the relation between "dorsal" and "ventral" cortical compartments is emphasized; the amygdala, hippocampus, and pregenual anterior cingulate are implicated in the pathophysiology of MD and are potential targets for treatment. The neuroanatomy of psychiatric neurosurgical procedures and related neuroimaging findings are reviewed. Finally, anticipated future directions of research in this field are discussed.

The relationship of age to prepulse inhibition and habituation of the acoustic startle response

Prepulse inhibition (PPI) of the startle response reflects an early stage of information processing that is abnormal in schizophrenia and certain other specific neuropsychiatric disorders that are distinguished by the inability to inhibit redundant or relatively irrelevant sensory, cognitive, or motor information. The goal of the present study was to characterize the effect of normal aging on PPI and habituation of the startle response and to examine the hypothesis that normal aging is characterized by a global decline in inhibitory function. Ninety-seven non-psychiatric controls (age range 18-88) were tested for startle eyeblink response using electromyogram (EMG) recording. Startle magnitude decreased and startle latency increased with aging. PPI demonstrated an inverted U-shaped function with age (greatest PPI at intermediate ages) while there was no significant effect of age on startle habituation. The results do not support the theory that aging is associated with a general decline in inhibitory function and contrast with previous studies that have compared only extreme age groups and have found no effects of age on PPI.

Opposite metabolic changes in the habenula and ventral tegmental area of a genetic model of helpless behavior

Congenitally helpless rats have been selectively bred to display an immediate helpless response to stress in order to model hereditary brain differences that contribute to depression vulnerability. Differences in regional brain metabolism between congenitally helpless and non-helpless rats were investigated using quantitative cytochrome oxidase histochemistry. The results indicated that congenitally helpless rats had 64-71% elevated metabolism in the habenula and a 25% elevation in the related interpeduncular nucleus. In contrast, helpless rats had 28% reduced metabolism in the ventral tegmental area (VTA) and 14-16% reductions in the basal ganglia and basolateral and central amygdala. The opposite metabolic changes in the habenula and ventral tegmental area may be especially important for determining the congenitally helpless rat's global pattern of brain activity, which resembles the metabolic activity pattern produced by dopamine antagonism.

The effects of neuroleptic medications on basal ganglia blood flow in schizophreniform disorders: a comparison between the neuroleptic-naïve and medicated states

BACKGROUND

Previous studies indicate that basal ganglia volumes of first-episode neuroleptic-naïve patients with schizophrenia are smaller than those of normal control subjects. Subsequent exposure to neuroleptic medication appears to induce volumetric change. Possible reasons for this include differences in blood flow and metabolism between the neuroleptic-naïve and medicated states.

METHODS

We used positron emission tomography (PET) to measure blood flow to the caudate and putamen, in a sample of 29 neuroleptic-naïve patients with schizophreniform disorders and 29 matched control subjects. We also studied a subset of the patient sample (n = 13), comparing their "before" versus "on" medication PET scans.

RESULTS

We did not find a significant difference in blood flow to the caudate and putamen between neuroleptic-naïve patients and control subjects even after controlling for whole brain blood flow; however, in the subset of 13 patients compared in the "on" versus "off" medication states, there was a statistically significant increase in blood flow to both the caudate and putamen.

CONCLUSIONS

Before treatment, there appears to be no difference in striatal blood flow between first-episode neuroleptic-naïve patients and healthy volunteers, but there appears to be a significant increase in blood flow to the striatum after the treatment is initiated.

Dopaminergic abnormalities in amygdaloid nuclei in major depression: a postmortem study

BACKGROUND

A deficiency of mesolimbic dopamine (DA) is a leading candidate for the etiology of certain symptoms of depression (e.g., anhedonia and loss of motivation). Here we show amounts of dopaminergic proteins in the amygdala, a key brain structure involved in the integration of emotions and stress, in subjects with major depression and in psychiatrically normal control subjects.

METHODS

The specific binding of [(125)I]RTI 55 to the DA transporter, [(3)H]SCH 23390 to the D1 receptor and [(125)I]epidepride to D2/D3 receptors were measured in the right amygdaloid complex in postmortem brains from 11 subjects with major depression and 11 matched control subjects.

RESULTS

The binding of [(125)I]RTI 55 to DA transporter was significantly lower in the basal and central amygdaloid nuclei, whereas the binding of [(125)I]epidepride to D2/D3 receptors was significantly higher in the basal, central, and lateral amygdaloid nuclei in major depression compared with control subjects. No difference in the binding of [(3)H]SCH 23390 to D1 receptors was observed.

CONCLUSIONS

Given that DA depletion in rats can induce a reduction in the DA transporter and an upregulation of D2/D3 receptors, our data are consistent with the hypothesis that major depression is associated with a deficiency of mesolimbic DA.

Reduced prepulse inhibition in rats with entorhinal cortex lesions

The relationship between the entorhinal cortex and prepulse inhibition (PPI) as well as dopaminergic participation in this relationship were examined. PPI is an operational measure of sensorimotor gating in which a robust response to a startling auditory pulse stimulus is inhibited when the stimulus is preceded by a weak prepulse. PPI can be measured in various species and is reduced in several neuropsychiatric disorders and in dopamine-activated rats. The entorhinal cortex was damaged bilaterally using ibotenic acid, and acoustic startle experiments were performed during treatment with haloperidol or saline on day 21 after the ibotenic acid injection. Neither this injection nor haloperidol affected the amplitude of the startle movement. Bilateral entorhinal cortex lesions reduced PPI, while haloperidol partially restored it. The entorhinal cortex and the sensorimotor gating system therefore may be related via dopaminergic circuits, possibly including the nucleus accumbens. Further, as the entorhinal cortex provides the major extrinsic synaptic input to the rat hippocampus, disease involvement of this region may severely affect cognition in various disorders including schizophrenia.

Dissociation in the involvement of dopaminergic neurons innervating the core and shell subregions of the nucleus accumbens in latent inhibition and affective perception

Mesencephalic dopaminergic neurons have been found to be involved in affective processes. Their implication in cognitive processes appears less well understood. The use of latent inhibition paradigms is a means of studying these kinds of processes. In this study, we investigated the involvement of dopaminergic projections in the core, the dorsomedial shell and the ventromedial shell of the nucleus accumbens, in latent inhibition in olfactory aversive learning. Variations in extracellular dopamine levels induced by an aversively conditioned olfactory stimulus were monitored in the three parts of the nucleus accumbens in the left hemisphere, after pre-exposure to the olfactory stimulus using in vivo voltammetry in freely moving rats. The parallel between dopamine changes and place preference or aversion toward the stimulus were analyzed in pre-exposed and non-pre-exposed animals. Results showed that dopaminergic neurons innervating the nucleus accumbens are differentially involved in the latent inhibition phenomenon. Dopaminergic neurons innervating the core and the dorsomedial shell subregions of the nucleus accumbens appeared to be involved in latent inhibition processes, unlike those reaching the ventromedial shell. Nonetheless dopamine in the ventromedial shell was found to be involved in affective perception of the stimulus.The present data suggest that dopaminergic neurons innervating the three nucleus accumbens subregions are functionally related to networks involved in parallel processing of the cognitive and affective values of environmental information, and that interaction between these systems, at some levels, may lead to a given behavioral output. These data may provide new insights into the pathophysiology of schizophrenic psychoses.

Dynamics of tyrosine hydroxylase promoter activity during midbrain dopaminergic neuron development

Dopamine (DA)-producing neurons in the ventral midbrain are generated from a specified neuronal lineage and form selective axonal pathways that mediate multiple CNS functions. Expression of the gene encoding tyrosine hydroxylase (TH), which is a key enzyme of catecholamine biosynthesis, is regulated during the development of midbrain DA neurons. In the present study, we report the developmental regulation and cell type specificity of TH gene promoter in the ventral midbrain by using a green fluorescent protein (GFP) reporter system. Transgenic mice were generated that express GFP in the majority of midbrain DA neurons under the control of the 9-kb upstream region of the rat TH gene. At an early embryonic stage, GFP expression was induced in the developing DA neurons, and the expression was then markedly down-regulated at later embryonic stages. However, the expression was reactivated and approached the adult levels during early post-natal development. These developmental changes in GFP expression patterns suggest the presence of multistep regulatory mechanisms for TH gene expression during DA neuron development. The TH promoter appears to possess transcriptional elements at least necessary for the induction of TH expression at the early embryonic stage and its reactivation during the post-natal development.

Repetitive transcranial magnetic stimulation increases the release of dopamine in the mesolimbic and mesostriatal system

Repetitive transcranial magnetic stimulation (rTMS) is suggested to be a potentially useful treatment in major depression. In order to optimize rTMS for therapeutic use, it is necessary to understand the neurobiological mechanisms involved, particularly the nature of the neurochemical changes induced. Using intracerebral microdialysis in urethane-anesthetized and conscious adult male Wistar rats, we monitored the effects of acute rTMS (20 Hz) on the intrahippocampal, intraaccumbal and intrastriatal release patterns of dopamine and its metabolites (homovanillic acid, 3,4-dihydroxyphenylacetic acid). The stimulation parameters were adjusted according to the results of accurate MRI-based computer-assisted reconstructions of the current density distributions induced by rTMS in the rat brain, ensuring stimulation of frontal brain regions. In the dorsal hippocampus, the shell of the nucleus accumbens and the dorsal striatum the extracellular concentration of dopamine was significantly elevated in response to rTMS. Taken together, these data provide the first in vivo evidence that acute rTMS of frontal brain regions has a modulatory effect on both the mesolimbic and the mesostriatal dopaminergic systems. This increase in dopaminergic neurotransmission may contribute to the beneficial effects of rTMS in the treatment of affective disorders and Parkinson's disease.

Hippocampal dysfunction in schizophrenia

Although not necessarily primary to the disease, hippocampal dysfunction in schizophrenia is suggested by morphological changes in the hippocampal formation reported in schizophrenic patients. This notion receives additional support from studies showing that 1) similar behavioral deficits are exhibited by both schizophrenics and animals with hippocampal lesions, and 2) some of these behavioral deficits are reversed by neuroleptics in both schizophrenics and lesioned animals. A brain-mapped neural network model is used to explain how some impairments in attention can be caused by hippocampal dysfunction and ameliorated by dopaminergic blockers.

Chronic, treatment-resistant depression and right fronto-striatal atrophy

BACKGROUND

Treatment-resistant depression (TRD) is relatively common but its neurobiological basis is poorly understood. Fronto-striatal structural brain changes have been reported in patients with depression but their association with treatment resistance and chronicity has not been established.

METHOD

Magnetic resonance images of 20 patients with TRD were compared with images of 20 recovered patients and 20 healthy controls. Images were compared using a voxel-based analysis (VBA) method; the results were validated by conventional volumetric analysis. The clinical associations of magnetic resonance imaging (MRI) changes with illness duration and severity were examined by VBA.

RESULTS

Only the TRD group exhibited right fronto-striatal atrophy, and subtle MRI changes in the left hippocampus on VBA. Atrophy was confirmed on volumetric analysis, the degree correlating with the cumulative number of electroconvulsive therapy (ECT) treatments received, suggesting an acquired deficit.

CONCLUSIONS

This is the first study to demonstrate fronto-striatal atrophy in patients with depression with poor outcome; the atrophy is more marked in those with more severe illness.

Selective immunolesioning of cholinergic neurons in nucleus basalis magnocellularis impairs prepulse inhibition of acoustic startle

Information processing and attentional abnormalities are prominent in neuropsychiatric disorders. Since the cholinergic neurons located in the nucleus basalis magnocellularis have been shown to be involved in attentional performance and information processing, recent efforts to analyze the significance of the basal forebrain in the context of schizophrenia have focused on this nucleus and its projections to the cerebral cortex. We report here that bilateral selective immunolesioning of the cholinergic neurons in the nucleus basalis magnocellularis is followed by significant deficits in sensorimotor gating measured by prepulse inhibition of the startle reflex in adult rats. This behavioral approach is used in both humans and rodents and has been proposed as a valuable model contributing to the understanding of the neurobiological substrates of schizophrenia. The disruption of prepulse inhibition persisted over repeated testing. The selective lesions were induced by bilateral intraparenchymal infusions of 192 IgG saporin at a concentration having minimal diffusion into adjacent nuclei of the basal forebrain. The infusions were followed by extensive loss of choline acetyltransferase-immunopositive neurons. Our results show that the cholinergic neurons of the nucleus basalis magnocellularis represent a critical station of the startle gating circuitry and suggest that dysfunction of these neurons may result in impaired sensorimotor gating characteristic of schizophrenia.

The role of neurotensin in the pathophysiology of schizophrenia and the mechanism of action of antipsychotic drugs

It has become increasingly clear that schizophrenia does not result from the dysfunction of a single neurotransmitter system, but rather pathologic alterations of several interacting systems. Targeting of neuropeptide neuromodulator systems, capable of concomitantly regulating several transmitter systems, represents a promising approach for the development of increasingly effective and side effect-free antipsychotic drugs. Neurotensin (NT) is a neuropeptide implicated in the pathophysiology of schizophrenia that specifically modulates neurotransmitter systems previously demonstrated to be dysregulated in this disorder. Clinical studies in which cerebrospinal fluid (CSF) NT concentrations have been measured revealed a subset of schizophrenic patients with decreased CSF NT concentrations that are restored by effective antipsychotic drug treatment. Considerable evidence also exists concordant with the involvement of NT systems in the mechanism of action of antipsychotic drugs. The behavioral and biochemical effects of centrally administered NT remarkably resemble those of systemically administered antipsychotic drugs, and antipsychotic drugs increase NT neurotransmission. This concatenation of findings led to the hypothesis that NT functions as an endogenous antipsychotic. Moreover, typical and atypical antipsychotic drugs differentially alter NT neurotransmission in nigrostriatal and mesolimbic dopamine (DA) terminal regions, and these effects are predictive of side effect liability and efficacy, respectively. This review summarizes the evidence in support of a role for the NT system in both the pathophysiology of schizophrenia and the mechanism of action of antipsychotic drugs.

A systems model of altered consciousness: integrating natural and drug-induced psychoses

Increasing evidence from neuroimaging and behavioral studies suggests that functional disturbances within cortico-striato-thalamic pathways are critical to psychotic symptom formation in drug-induced and possibly also naturally occurring psychoses. Recent basic and clinical research with psychotomimetic drugs, such as the N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, ketamine, and the serotonin-2A (5-HT(2A)) receptor agonist, psilocybin, suggest that the hallucinogenic effects of these drugs arise, at least in part, from their common capacity to disrupt thalamo-cortical gating of external and internal information to the cortex. Deficient gating of sensory and cognitive information is thought to result in an overloading inundation of information and subsequent cognitive fragmentation and psychosis. Cross-species studies of homologues gating functions, such as prepulse inhibition of the startle reflex, in animal and human models of psychosis corroborate this view and provide a translational testing mechanism for the exploration of novel pathophysiologic and therapeutic hypotheses relevant to psychotic disorders, such as the group of schizophrenias.

Pathophysiologische und neuropsychologische Aspekte depressiver Störungen

Zusammenfassung: Bei depressiven Störungen sind zahlreiche neurobiologische Auffälligkeiten dokumentiert. Aufschluß darüber geben Untersuchungen bei primärer Depression sowie Untersuchungen bei depressiven Störungen, die sich im Zusammenhang mit Hirnschädigungen, wie etwa Schlaganfällen, manifestieren. Ebenfalls lassen neuropsychologische Befunde Rückschlüsse auf pathophysiologische Mechanismen zu. Vieles deutet darauf hin, daß es bei depressiven Störungen zu einer Störung eines komplexen neuronalen Netzwerkes kommt, insbesondere unter Beteiligung präfrontaler cortikaler Strukturen, der Amygdala und der Basalganglien sowie ihrer monoaminergen Afferenzen aus Hirnstamm und pontinem Tegmentum. Der Befund eines reduzierten Hippokampusvolumens bei Subtypen der Depression geht möglicherweise auf einen Hypercortisolismus zurück. Neurobiologische Auffälligkeiten stellen einen wichtigen Anknüpfungspunkt für antidepressive Therapien dar. Insgesamt ist die Depression als eine psychobiologische Störung konzeptualisierbar, bei der biologische und psychologische Faktoren eng miteinander verzahnt sind.

Validating cortical surface analysis of medial prefrontal cortex

This paper describes cortical analysis of 19 high resolution MRI subvolumes of medial prefrontal cortex (MPFC), a region that has been implicated in major depressive disorder. An automated Bayesian segmentation is used to delineate the MRI subvolumes into cerebrospinal fluid (CSF), gray matter (GM), white matter (WM), and partial volumes of either CSF/GM or GM/WM. The intensity value at which there is equal probability of GM and GM/WM partial volume is used to reconstruct MPFC cortical surfaces based on a 3-D isocontouring algorithm. The segmented data and the generated surfaces are validated by comparison with hand segmented data and semiautomated contours, respectively. The L(1) distances between Bayesian and hand segmented data are 0.05-0.10 (n = 5). Fifty percent of the voxels of the reconstructed surface lie within 0.12-0.28 mm (n = 14) from the semiautomated contours. Cortical thickness metrics are generated in the form of frequency of occurrence histograms for GM and WM labelled voxels as a function of their position from the cortical surface. An algorithm to compute the surface area of the GM/WM interface of the MPFC subvolume is described. These methods represent a novel approach to morphometric chacterization of regional cortex features which may be important in the study of psychiatric disorders such as major depression.

Behavioral effects of psychomotor stimulants in rats with dorsal or ventral subiculum lesions: locomotion, cocaine self-administration, and prepulse inhibition of startle

Compelling evidence suggests a primary role for the mesoaccumbens dopaminergic pathway in the behavioral effects of amphetamine and cocaine, but the roles of other projections to the accumbens, including those arising in the hippocampal formation, are less clear. The authors evaluated the effects of discrete excitotoxic lesions of either the dorsal or ventral subiculum on the locomotor activating, reinforcing, and sensorimotor gating-disruptive effects of psychomotor stimulant drugs. Whereas dorsal subiculum-lesioned rats were hyperactive in tests of exploratory locomotion and startle reactivity, ventral subiculum-lesioned rats exhibited an attenuated locomotor response to amphetamine, moderately impaired acquisition of cocaine self-administration, and reduced levels of prepulse inhibition of startle. These 2 behavioral profiles overlap considerably with those previously observed in rats with lesions of the rostrodorsal and caudomedial accumbens, respectively, and suggest that projections from dorsal subiculum to accumbens core and ventral subiculum to accumbens shell exert distinct influences on behavioral responses that are amplified by psychomotor stimulant drugs.

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.

Neuroimaging and neuropathological studies of depression: implications for the cognitive-emotional features of mood disorders

Neuroimaging technology has provided unprecedented opportunities for elucidating the anatomical correlates of major depression. The knowledge gained from imaging research and from the postmortem studies that have been guided by imaging data is catalyzing a paradigm shift in which primary mood disorders are conceptualized as illnesses that involve abnormalities of brain structure, as well as of brain function. These data suggest specific hypotheses regarding the neural mechanisms underlying pathological emotional processing in mood disorders. They particularly support a role for dysfunction within the prefrontal cortical and striatal systems that normally modulate limbic and brainstem structures involved in mediating emotional behavior in the pathogenesis of depressive symptoms.

Translating the basic and clinical cognitive neuroscience of schizophrenia to drug development and clinical trials of antipsychotic medications

Neurocognitive deficits have become increasingly important defining features of schizophrenia and its treatment. Multiple domains of neurocognitive functions are impaired in schizophrenia patients, and these impairments are considered to be core features of the disorder. Many recent reports support the importance of the relationship of these neurocognitive deficits to measures of "functional outcome" such as social skills acquisition, social problem solving, and community outcome. Neurocognitive deficits appear to be improved with newer (atypical) antipsychotic medications across a broad range of domains in schizophrenia patients. Together with clinical neuroscience advances, basic research in cognitive neuroscience ranging from animal models of gating functions to early gene expression induced by antipsychotic medications has illuminated the specific neural basis of neurocognitive deficits in schizophrenia and the neurobiology of antipsychotic actions. These translational basic and clinical studies provide powerful screening tools and strategies for drug development and the subsequent assessment of the clinical efficacy of new antipsychotic medications. These interlocking clinical and basic research findings have substantial implications for improving both drug development and improving clinical trials methodology for antipsychotic medications. Thus, there is an informed translation and cross-fertilization between basic and clinical research focused on the development and assessment of putative new antipsychotic compounds.

Novelty-evoked elevations of nucleus accumbens dopamine: dependence on impulse flow from the ventral subiculum and glutamatergic neurotransmission in the ventral tegmental area

In vivo microdialysis in freely moving rats was used to monitor novelty-evoked elevations in extracellular dopamine in the nucleus accumbens septi (NAS) and to examine the role of the ventral subiculum of the hippocampus and glutamatergic transmission in the ventral tegmental area (VTA) on these elevations. Exposure to novel stimuli evoked investigatory activity and increased nucleus accumbens dopamine. Unilateral injections of the sodium channel blocker tetrodotoxin (0.16 ng/0.5 microL) into the ventral subiculum ipsilateral to the dialysed NAS abolished novelty-evoked elevations in dopamine. Injections of tetrodotoxin into the contralateral VS did not prevent novelty-evoked elevations in nucleus accumbens dopamine. Unilateral perfusion (via microdialysis) of the ionotropic glutamate receptor antagonists kynurenic acid (1 mM) into the ipsilateral but not the contralateral VTA blocked novelty-evoked elevations in nucleus accumbens dopamine. Neither unilateral injections of tetrodotoxin nor unilateral perfusion of kynurenic acid disrupted investigatory behaviour. These data indicate that phasic elevations in nucleus accumbens dopamine evoked by exposure to unconditioned novel stimuli are dependent on impulse flow from the hippocampus and glutamatergic transmission in the VTA.

Nucleus accumbens, entorhinal cortex and latent inhibition: a neural network model

A neural network model of classical conditioning (Schmajuk, Lam, and Gray, J. Exp. Psychol.: Anim. Behav. Process, 22, 1996, 321-349) is applied to the description of the neural substrates of latent inhibition. Experimental data suggest that latent inhibition might be controlled by a circuit that involves the hippocampus, the entorhinal cortex, the nucleus accumbens, and the mesolimbic dopaminergic projection from the ventral tegmental area to the accumbens. By mapping different nodes and connections in the model onto this brain circuit, computer simulations demonstrate that, in most cases, the model provides a good quantitative description of: (1) the impairment of latent inhibition by lesions of the shell of the nucleus accumbens; (2) the restoration of latent inhibition by haloperidol following lesions of the shell; (3) the preservation of latent inhibition by lesions of the core of the nucleus accumbens; (4) the facilitation of latent inhibition by combined shell core lesions and by core lesions with extended conditioning; (5) the impairment of latent inhibition following lesions of the entorhinal cortex or the hippocampus; and (6) the restoration of latent inhibition by haloperidol following lesions of the entorhinal cortex and ventral subiculum. In addition, the model is able to describe neural activity in the nucleus accumbens.

Tonic opioid inhibition of the subiculo-accumbens pathway

There is evidence to suggest that medium spiny neurons (MSNs) in the nucleus accumbens (NAS) should be sensitive to opiate compounds. However, neuronal responses in the NAS evoked by fimbria stimulation (F-D) are insensitive to systemically or iontophoretically administered morphine. The hypothesis of this study was that fimbria-evoked NAS responses may fail to demonstrate sensitivity to morphine because they are under tonic opioid inhibition and can't be further inhibited by opiates. If correct, then pharmacological inhibition of opioid actions on these NAS neuronal responses should result in an increase of response to fimbria stimulation. The effects of systemic and iontophoretic administrations of naloxone on NAS responses evoked by fimbria stimulation were observed. Systemically and locally administered naloxone selectively increased the excitability of accumbens single-unit responses to fimbria stimulation. Conversely, systemic or iontophoretic administration of morphine was without effect on the same types of NAS responses. These observations are consistent with the hypothesis that a tonic opioid inhibition may regulate this pathway. In contrast, naloxone and morphine effect other NAS circuit responses differently than F-D NAS responses. In some cases naloxone and morphine tests have been conducted on different evoked responses from the same neuron. Those results have shown that different responses from the same cell may be differentially affected. Consequently, opioid modulation of activity in the NAS is probably pathway-specific rather than neuron-specific.

Schizophrenia patients demonstrate a dissociation on declarative and non-declarative memory tests

Declarative memory refers to the recall and recognition of factual information. In contrast, non-declarative memory entails a facilitation of memory based on prior exposure and is typically assessed with priming and perceptual-motor sequencing tasks. In this study, schizophrenia patients were compared to normal comparison subjects on two computerized memory tasks: the Word-stem Priming Test (n=30) and the Pattern Sequence Learning Test (n=20). Word-stem Priming includes recall, recognition (declarative) and priming (non-declarative) components of memory. The schizophrenia patients demonstrated an impaired performance on recall of words with relative improvement during the recognition portion of the test. Furthermore, they performed normally on the priming portion of the test. Thus, on tests of declarative memory, the patients had retrieval deficits with intact performance on the non-declarative memory component. The Pattern Sequence Learning Test utilizes a serial reaction time paradigm to assess non-declarative memory. The schizophrenia patients' serial reaction time was significantly slower than that of comparison subjects. However, the patients' rate of acquisition was not different from the normal comparison group. The data suggest that patients with schizophrenia process more slowly than normal, but have an intact non-declarative memory. The schizophrenia patients' dissociation on declarative vs. non-declarative memory tests is discussed in terms of possible underlying structural impairment.

Increases in manic symptoms after life events involving goal attainment

Bipolar disorder has been conceptualized as an outcome of dysregulation in the behavioral activation system (BAS), a brain system that regulates goal-directed activity. On the basis of the BAS model, the authors hypothesized that life events involving goal attainment would promote manic symptoms in bipolar individuals. The authors followed 43 bipolar I individuals monthly with standardized symptom severity assessments (the Modified Hamilton Rating Scale for Depression and the Bech-Rafaelsen Mania Rating Scale). Life events were assessed using the Goal Attainment and Positivity scales of the Life Events and Difficulties Schedule. As hypothesized, manic symptoms increased in the 2 months following goal-attainment events, but depressed symptoms were not changed following goal-attainment events. These results are congruent with a series of recent polarity-specific findings.

3D MRI studies of neuroanatomic changes in unipolar major depression: the role of stress and medical comorbidity

Increasing evidence has accumulated for structural brain changes associated with unipolar recurrent major depression. Studies of neuroanatomic structure in early-onset recurrent depression have only recently found evidence for depression-associated structural change. Studies using high-resolution three-dimensional magnetic resonance imaging (MRI) are now available to examine smaller brain structures with precision. Brain changes associated with early-onset major depression have been reported in the hippocampus, amygdala, caudate nucleus, putamen, and frontal cortex, structures that are extensively interconnected. They comprise a neuroanatomic circuit that has been termed the limbic-cortical-striatal-pallidal-thalamic tract. Of these structures, volume loss in the hippocampus is the only consistently observed change to persist past the resolution of the depression. Possible mechanisms for tissue loss include neuronal loss through exposure to repeated episodes of hypercortisolemia; glial cell loss, resulting in increased vulnerability to glutamate neurotoxicity; stress-induced reduction in neurotrophic factors; and stress-induced reduction in neurogenesis. Many depressed patients, particularly those with late-onset depression, have comorbid physical illnesses producing a high rate of hyperintensities in deep white matter and subcortical gray matter and brain damage to key structures involved in the modulation of emotion. Combining MRI studies with functional studies has the potential to localize abnormalities in blood flow, metabolism, and neurotransmitter receptors and provide a better integrated model of depression.

A neural model of working memory processes in normal subjects, Parkinson's disease and schizophrenia for fMRI design and predictions

A computational model was previously developed to investigate the role of parallel basal ganglia-thalamocortical loops in solving tasks that rely on working memory. Different lesions are applied to the model in order to investigate the working memory deficits observed in Parkinson's disease and schizophrenia. The simulations predict that the working memory deficits observed in Parkinson's disease result from a local dysfunction within the brain due to a problem in the disinhibitory process arising from the basal ganglia. They also predict that the working memory deficits observed in schizophrenia involve many cortical and subcortical areas and result from a problem in selecting items in working memory which are stored in basal ganglia-thalamocortical loops. The simulations predict the temporal unfolding of neuronal activity in different brain regions, both in the normal case and in the two disease states. A specific event-related functional magnetic resonance imaging study was elaborated to test some of those predictions.

Electrophysiological evidence for reduced latent inhibition in schizophrenic patients

The present study examined latent inhibition (LI) effects in 17 acute and 16 partially remitted schizophrenic patients, and in 20 healthy controls, by measuring manual response latencies and event-related potentials (ERPs) during an association learning task. ERPs were recorded to elucidate the role of attention in the LI effect. Subjects performed a go/no-go task with an auditory conditional stimulus predicting a visual go command. Half of the subjects in each diagnostic group were pre-exposed to the conditional stimulus which had been used as an irrelevant distractor in a preceding discrimination task. Independent of diagnostic group membership, pre-exposed subjects showed slower manual responses to go stimuli than non-pre-exposed subjects, reflecting a robust LI effect. The N100 wave after the conditional stimuli, however, showed a differential pattern: pre-exposure increased N100 amplitudes in acute schizophrenics, whereas pre-exposed control subjects showed a trend for decreased N100. The amplitude of the contingent negative variation (CNV) was unaffected by pre-exposure. The ERP results suggest that acute schizophrenics have a deficit in learned inattention to irrelevant stimuli. However, the intact LI effect in schizophrenics at the motor speed level shows that human LI is a complex phenomenon depending on the tasks and measures used.

Dopaminergic modulation of neuronal excitability in the striatum and nucleus accumbens

The striatum and its ventral extension, the nucleus accumbens, are involved in behaviors as diverse as motor planning, drug seeking, and learning. Invariably, these striatally mediated behaviors depend on intact dopaminergic innervation. However, the mechanisms by which dopamine modulates neuronal function in the striatum and nucleus accumbens have been difficult to elucidate. Recent electrophysiological studies have revealed that dopamine alters both voltage-dependent conductances and synaptic transmission, resulting in state-dependent modulation of target cells. These studies make clear predictions about how dopamine, particularly via D1 receptor activation, should alter the responsiveness of striatal neurons to extrinsic excitatory synaptic activity.

Functional neuroimaging and the neuroanatomy of obsessive-compulsive disorder

Functional neuroimaging studies have advanced the understanding of the brain mediation of OCD by orbitofrontal-subcortical circuitry, but much is still unknown. Phenotypic heterogeneity could account for many of the inconsistencies among previous neuroimaging studies of OCD. Current studies are seeking to find the neurobiological basis of OCD symptom subtypes and predictors of treatment response. Future studies combining genetics and basic neuroanatomic research with neuroimaging may clarify the cause and pathophysiology of OCD. Although many lines of evidence point to dysfunction of orbitofrontal-subcortical circuitry in patients with OCD, many questions remain unanswered. Some have suggested that orbitofrontal-subcortical hyperactivity in OCD may be the result of abnormal neuroanatomic development of these structures or a failure of pruning of neuronal connections between them, as occurs in normal development, but no postmortem neuroanatomic studies of OCD exist to delineate its pathophysiology. Interventions that directly alter the indirect-direct pathway balance within frontal-subcortical circuits will allow for direct testing of the pathophysiologic hypotheses presented here. The roles of various neurochemical systems in OCD are similarly unclear. Although an abundance of indirect evidence suggests serotonergic abnormalities in patients with OCD, no direct evidence demonstrates what those abnormalities are or whether they are primary or secondary phenomena in patients with OCD. Ongoing studies of 5-HT synthesis in the brains of patients with OCD may shed light on this question.

A role for glutamate transmission in addiction to psychostimulants

Abstract Psychostimulant addiction results in the emergence of undesirable behaviors such as drug craving and paranoia. Using animal models of addiction the neurobiological substrates mediating these behaviors have been examined. Studies have focused on cellular adaptations within the motive circuit that contains the nucleus accumbens, ventral tegmental area, ventral pallidum and prefrontal cortex. While long-term alterations in dopamine transmission have been clearly characterized, more recent studies reveal that important neuroadaptations are also produced in glutamate transmission.This short review provides a description of these neuroadaptations and a discussion of how these psychostimulant-induced changes may synergize to elicit addiction-related behaviors.

The connections of the dopaminergic system with the striatum in rats and primates: an analysis with respect to the functional and compartmental organization of the striatum

This Commentary compares the connections of the dopaminergic system with the striatum in rats and primates with respect to two levels of striatal organization: a tripartite functional (motor, associative and limbic) subdivision and a compartmental (patch/striosome-matrix) subdivision. The topography of other basal ganglia projections to the dopaminergic system with respect to their tripartite functional subdivision is also reviewed. This examination indicates that, in rats and primates, the following observations can be made. (1) The limbic striatum reciprocates its dopaminergic input and in addition innervates most of the dopaminergic neurons projecting to the associative and motor striatum, whereas the motor and associative striatum reciprocate only part of their dopaminergic input. Therefore, the connections of the three striatal subregions with the dopaminergic system are asymmetrical, but the direction of asymmetry differs between the limbic versus the motor and associative striatum. (2) The limbic striatum provides the main striatal input to dopamine cell bodies and proximal dendrites, with some contribution from a subset of neurons in the associative and motor striatum (patch neurons in rats; an unspecified group of neurons in primates), while striatal input to the ventrally extending dopamine dendrites arises mainly from a subset of neurons in the associative and motor striatum (matrix neurons in rats; an unspecified group of neurons in primates). (3) Projections from functionally corresponding subdivisions of the striatum, pallidum and subthalamic nucleus to the dopaminergic system overlap, but the specific targets (dopamine cells, dopamine dendrites, GABA cells) of these projections differ. Major differences include the following. (1) In rats, neurons projecting to the motor and associative striatum reside in distinct regions, while in primates they are arranged in interdigitating clusters. (2) In rats, the terminal fields of projections arising from the motor and associative striatum are largely segregated, while in primates they are not. (3) In rats, patch- and matrix-projecting dopamine cells are organized in spatially, morphologically, histochemically and hodologically distinct ventral and dorsal tiers, while in primates there is no (bi)division of the dopaminergic system that results in two areas which have all the characteristics of the two tiers in rats. Based on the anatomical data and known dopamine cell physiology, we forward an hypothesis regarding the influence of the basal ganglia on dopamine cell activity which captures at least part of the complex interplay taking place within the substantia nigra between projections arising from the different basal ganglia nuclei. Finally, we incorporate the striatal connections with the dopaminergic system into an open-interconnected scheme of basal ganglia-thalamocortical circuitry.

Nicotine, brain nicotinic receptors, and neuropsychiatric disorders

Neuronal nicotinic acetylcholine receptors (nAChRs) represent a large family of ligand-gated cation channels with diverse structures and properties. In contrast to the muscular nAChRs, the physiological functions of neuronal nAChRs are not well defined to date. Behavioral studies indicate that brain nAChRs participate in complex functions such as attention, memory, and cognition, whereas clinical data suggest their involvement in the pathogenesis of certain neuropsychiatric disorders (Alzheimer's and Parkinson's diseases, Tourette's syndrome, schizophrenia, depression, etc.). For the majority of these disorders, the use of nAChRs' agonists may represent either a prophylactic (especially for Alzheimer's and Parkinson's diseases) or a symptomatic treatment. The possible mechanisms underlying these beneficial effects as well as the characteristics and potential therapeutic use of new, subtype-selective nAChRs agonists are presented.

Basal ganglia and cerebellar loops: motor and cognitive circuits

The traditional view that the basal ganglia and cerebellum are simply involved in the control of movement has been challenged in recent years. One of the pivotal reasons for this reappraisal has been new information about basal ganglia and cerebellar connections with the cerebral cortex. In essence, recent anatomical studies have revealed that these connections are organized into discrete circuits or 'loops'. Rather than serving as a means for widespread cortical areas to gain access to the motor system, these loops reciprocally interconnect a large and diverse set of cerebral cortical areas with the basal ganglia and cerebellum. The properties of neurons within the basal ganglia or cerebellar components of these circuits resembles the properties of neurons within the cortical areas subserved by these loops. For example, neuronal activity within basal ganglia and cerebellar loops with motor areas of the cerebral cortex is highly correlated with parameters of movement, while neuronal activity within basal ganglia and cerebellar loops with areas of the prefrontal cortex is more related to aspects of cognitive function. Thus, individual loops appear to be involved in distinct behavioral functions. Studies of basal ganglia and cerebellar pathology support this conclusion. Damage to the basal ganglia or cerebellar components of circuits with motor areas of cortex leads to motor symptoms, whereas damage of the subcortical components of circuits with non-motor areas of cortex causes higher-order deficits. In this report, we review some of the new anatomical, physiological and behavioral findings that have contributed to a reappraisal of function concerning the basal ganglia and cerebellar loops with the cerebral cortex.

Set-maintenance and set-shifting problems in schizophrenic subtypes: relationship to dysfunctions of the fronto-striatal loops

Research with patients suffering from Parkinson's disease and frontal lobe lesions has shown that disturbances in the fronto-striatal loops in the brain can cause perseveration. Perseveration is a core symptom of schizophrenia, yet the cause is not known. For schizophrenic patients disorders of many parts of the fronto-striatal loops are found, for example disturbances of the prefrontal cortex and the striatum. Perseveration in schizophrenia can be explained with set-maintenance problems, related to dysfunction of the prefrontal cortex, or with set-shifting problems that are related to disorders in the striatum. These set-maintenance and set-shifting problems can be distinguished with neuropsychological tests. Regarding the bloodflow patterns for the different subtypes of schizophrenia three problems are expected as explanations for perseveration: set-maintenance problems concerning abstract information, set-maintenance problems shifting between stimuli and enhanced set-shifting with cues.

Basal ganglia output and cognition: evidence from anatomical, behavioral, and clinical studies

The traditional view that the basal ganglia are simply involved in the control of movement has been challenged in recent years. Three lines of evidence indicate that the basal ganglia also are involved in nonmotor operations. First, the results of anatomical studies clearly indicate that the basal ganglia participate in multiple circuits or 'loops' with cognitive areas of the cerebral cortex. Second, the activity of neurons within selected portions of the basal ganglia is more related to cognitive or sensory operations than to motor functions. Finally, in some instances basal ganglia lesions cause primarily cognitive or sensory disturbances without gross motor impairments. In this report, we briefly review some of these data and present a new anatomical framework for understanding the basal ganglia contributions to nonmotor function.

Influence of stimulus control on the excitability of the electrically elicited blink reflex in patients with schizophrenia

BACKGROUND

In humans, the excitability of the electrically evoked blink reflex is influenced by the subject's attention to the stimulus. The early reflex component R1 has been found to be facilitated in conditions of increased selective attention, whereas the late components R2 and R3 exhibited a marked suppression. Distraction from the stimulus leads to enhanced R2 and R3 magnitudes.

METHODS

We investigated the excitability of the distinct reflex components in 19 patients with schizophrenia and 19 healthy control subjects. In the control condition (EE), stimulation was elicited by the experimenter; in a second condition (SE), subjects released a key to evoke the reflex themselves.

RESULTS

The SE patients with schizophrenia exhibited an abnormally increased R1 facilitation and an impaired R2 inhibition in comparison with normal control subjects. An R3 component could be registered in EE in 13 of 19 patients but only in one control subject; SE resulted in a complete suppression of this component in all but two patients with schizophrenia.

CONCLUSIONS

The abnormal R1 facilitation and the impaired R2 inhibition may be regarded as neurophysiological markers of defective information processing in a condition of increased selective attention to a self-controlled stimulus in patients with schizophrenia. The enhanced excitability of the R3 component under standard conditions indicates defective attentional mechanisms in patients with schizophrenia in an uninstructed passive condition attending a stimulus triggered by the experimenter.