Browsing by Author "Exner, C."

The authors sought to clarify whether lesions in different parts of the cerebellum result in differential cognitive and affective impairment. Six subjects with cerebellar lesions due to posterior inferior cerebellar artery ( PICA) infarction, five subjects with lesions in the SCA vascular territory, and 11 matched controls were administered a battery of standard neuropsychological tests. PICA lesions but not SCA lesions resulted in cognitive and affective deficits pointing to a dominant role of posterior cerebellar regions in cognitive and affective processing.

Transcranially applied weak direct currents are capable of modulating motor cortical excitability in the human. Anodal stimulation enhances excitability, cathodal stimulation diminishes it. Cortical excitability changes accompany motor learning. Here we show that weak direct currents are capable of improving implicit motor learning in the human. During performance of a serial reaction time task, the primary motor cortex, premotor, or prefrontal cortices were stimulated contralaterally to the performing hand. Anodal stimulation of the primary motor cortex resulted in increased performance, whereas stimulation of the remaining cortices had no effect. We conclude that the primary motor cortex is involved in the acquisition and early consolidation phase of implicit motor learning.

individuals with schizophrenia have difficulties in emotional information processing. A relationship between behavioral variables of emotional processing and structural amygdala alterations in schizophrenia has been proposed but not shown, yet. Morphological studies of amygdala size in schizophrenia have yielded inconsistent results. The current study assessed paired associates learning of emotional and neutral faces in 16 subjects with schizophrenia during acute episode and in relative remission after 3 months. Sixteen matched controls were studied for comparison. Subjects also underwent structural magnetic resonance imaging (3D-MRI) at the first time of assessment. Subjects with schizophrenia showed a significant decrease (by 13%) in total size of the amygdala compared to controls, which was more pronounced on the right side. Subjects with schizophrenia improved associative learning of facial identities but not of emotional facial expressions after relative remission of psychotic symptoms. Volume of the right amygdala in subjects with schizophrenia and in controls was significantly related to emotional learning, indicating better learning in subjects with larger amygdala size. Our results indicate that subjects with schizophrenia have a deficit to form associations when emotionally loaded material is used. This deficit seems to be trait-like and independent of disease state. It seems to be linked to size reduction of the right amygdala in schizophrenia. (C) 2004 Elsevier B.V. All rights reserved.

Background: Lesions of the thalamus interfere with cognitive functions mainly in the area of declarative learning and memory. Little is known about the role the thalamus plays in implicit learning. Objective: To study explicit and implicit learning and memory in subjects with thalamic lesions and to analyze the influence of lesion characteristics on cognitive performance. Methods: The authors studied the performance of 15 subjects with focal thalamic infarction or hemorrhage on a comprehensive neuropsychological test battery focusing on tests of explicit memory and learning of a nondeclarative motor skill. Subjects with thalamic lesions were compared to 15 healthy matched control subjects and to a clinical control group of 22 subjects who had sustained basal ganglia lesions. Results: Subjects with thalamic lesions showed well-preserved intellectual and executive functions but demonstrated deficits on measures of attention and psychomotor speed, explicit memory, and implicit visuomotor sequence learning. Lesion size in the thalamus was clearly related to subjects' long-term explicit memory performance. However, few of the neuropsychological deficits found seemed specific to the long-term neuropsychological outcome of focal thalamic infarctions. Subjects with lesions in the basal ganglia demonstrated similar deficits. Conclusions: Focal subcortical lesions in the thalamus and the basal ganglia lead to a similar profile of neuropsychological deficits. Lesions in the thalamus not only affect declarative memory but also interfere with nondeclarative motor skill learning.

The search for a special neuropsychological profile of frontal lobe epilepsy subjects (FLE) has so far led to inconclusive results. In this paper we compared the preoperative neuropsychological performance of FLE and temporal lobe epilepsy (TLE) subjects. We further investigated whether frontal lobe lesions of epileptogenic cause produce the same type of cognitive dysfunction as do tumours of the frontal lobe. Sixteen FLE subjects were compared to 16 TLE subjects as well as to a group of 10 subjects after the removal of frontal lobe tumors (TUM) and a healthy control group, A set of neuropsychological test measures routinely used for presurgical evaluation, an emotional conceptualization task and two associative learning tasks were administered. We found that subjects with frontal lobe damage were significantly impaired relative to controls on a wide range of cognitive functions independent of neurological cause. FLE subjects could hardly be discriminated from TLE subjects as both groups showed a similarly reduced level of neuropsychological performance. Our results demonstrate the devastating effect that frontal lobe epilepsy can have on cognitive functioning. Routinely used neuropsychological test measures lack the specificity to distinguish between frontal and temporal lobe epilepsy. Highly specialized measures are necessary to reveal differences. (C) 2002 BEA Trading Ltd.

Increasing evidence suggests that schizophrenia is associated with various morphological and functional abnormalities of the frontal cortex. So far research has concentrated on the dorsolateral and orbitofrontal cortex. Behavioral evidence suggests however that regions responsible for higher motor control are compromised in schizophrenia as well. The current study assessed volumes of the anterior supplementary motor area (pre-SMA) and implicit motor sequence learning in 15 subjects with first-episode schizophrenia and 15 healthy matched controls. Pre-SMA volumes were assessed by three-dimensional structural magnetic resonance imaging (3D-MRI) and manual parcellation according to an established protocol. Implicit motor sequence learning was assessed using the Serial Reaction-Time Task (SRTT). Compared with control subjects, schizophrenia subjects had significantly smaller volumes of the left pre-SNIA (16%). Subjects with schizophrenia were severely impaired on sequence-specific implicit motor learning. Size of the left pre-SNIA of schizophrenia subjects was significantly related to impaired implicit learning. We conclude that subjects with first-episode schizophrenia have a morphological abnormality of the left pre-SMA that might predispose them to develop disturbances of higher motor control during acute episodes of psychosis. These structural and behavioral abnormalities might be conceptualized within a broader model that views schizophrenia as a disorder of disturbed coordination of thought and action. (c) 2006 Elsevier B.V. All rights reserved.

Previous research has confirmed stable explicit memory deficits in schizophrenia across disease states. However, little is known about the implicit learning capabilities of individuals with schizophrenia across the course of illness. The current study assessed procedural learning in 19 schizophrenia subjects (DSM-IV criteria) and 19 matched controls using the Serial Reaction-Time Task (SRTT). The severity of negative, positive and disorganized symptoms was assessed using the Scales for the Assessment of Positive and Negative Symptoms. A sub-sample of II schizophrenia subjects and II controls was reassessed 20 months later when symptoms in the schizophrenia subjects had largely remitted. Schizophrenia subjects were severely impaired on sequence-specific procedural learning during an acute episode. This deficit could not be explained by a general memory or processing speed impairment. Impaired implicit learning scores were significantly related to higher ratings of disorganized symptoms. However, 20 months later, when acute symptoms had remitted, the performance of the schizophrenia subjects on procedural learning had normalized. Our findings might share a conceptual overlap with previous reports of a reduced ability of schizophrenia subjects during an acute episode to adapt ongoing perceptual and behavioral programs to previously experienced regularities in their environment. (c) 2005 Elsevier Ireland Ltd. All rights reserved.

There has been a growing interest in the differential role of various neural structures in implicit learning processes. The goal of our study was to clarify how focal lesions restricted to the basal ganglia interfere with different aspects of implicit visuo-motor sequence learning. A version of the Serial Reaction Time Task (SRTT) of Nissen and Bullemer using a 12-trial sequence was administered. A total of 20 subjects with focal basal ganglia lesions caused by ischemic or hemorrhagic infarction and 20 matched control subjects participated in this study. The results indicate that subjects with focal basal ganglia lesions showed unimpaired implicit learning of a 12-item motor sequence. Subjects with basal ganglia lesions, however, had more difficulties improving their general proficiency with the reaction-time task independent of sequence-specific learning. We observed a tendency toward smaller regional volumes in the cerebellum and left pre-supplementary motor area (pre-SMA) of subjects with basal ganglia lesions. Smaller cerebellar and pre-SMA volumes were related to lower implicit learning performance in the lesion group. The size of lesions in the basal ganglia was not related to sequence-specific implicit learning but had a significant influence on subjects' general proficiency for execution of the reaction-time task. We propose that implicit learning is achieved by a distributed network of cortical and subcortical structures. The basal ganglia seem to be responsible for adjusting to the general requirements of a task rather than for learning specific associations between stimuli that might be accomplished by premotor frontal areas and the cerebellum instead.