Somatosensory discrimination of shape:prediction of success in normal volunteers and Parkinsonian patients

Tactile discrimination of macrogeometric objects in a two-alternative forced-choice procedure represents a complex task including somatosensory and higher-order cognitive processing. The objects for somatosensory discrimination were rectangular parallelepipeds that differed in oblongness only. They were presented in sequential pairs to 12 normal volunteers and 13 parkinsonian patients. Owing to the dichotomy of the task, we calculated estimates of the probability of a correct answer by a binomial approach. The probability of a correct answer could be calculated on the basis of a logistic model ensuring that the probability values lie in the interval [0, 1]. The relationship between the probability of a correct answer and the difference in oblongness of the objects could be described solely by one coefficient determined by logistic regression. This coefficient summarized the effectiveness of the simultaneous and consecutive operations inherent in the task and allowed characterization of performances in groups and individuals

Impaired somatosensory discrimination of shape in Parkinson's disease: Association with caudate nucleus dopaminergic function

Tactile discrimination of macrogeometric objects in a two-alternative forced-choice procedure represents a demanding task involving somatosensory pathways and higher cognitive processing. The objects for somatosensory discrimination, i.e., rectangular parallelepipeds differing only in oblongness, were presented in sequential pairs to normal volunteers and 12 parkinsonian patients. The performance of patients was significantly impaired compared to normal volunteers. From a biochemical point of view, the patients were characterized by a severely reduced 6-[F-18]-fluoro-L-dopa (FDOPA) tracer metabolism in the basal ganglia, as measured using positron emission tomography (PET). Furthermore, reduced specific FDOPA metabolism in the putamen was consistent with the impaired motor capacities of the patients. The reduced specific FDOPA-uptake within the caudate nucleus was associated with additionally diminished somatosensory discrimination. This association, of low perception during task performance and decreased FDOPA-uptake, provides direct evidence for the role of the caudate nucleus in the cognitive part of the task. We suggest that directed attention and working memory were critically involved as a result of disturbed interactions between the head of the caudate nucleus and the dorsolateral prefrontal cortex. Furthermore, there were indications of an additional involvement of the mesolimbic system, which might be of importance during challenging situations such as forced choice. We conclude that differential effects on parts of the basal ganglia, during evolution of the degenerative process characteristic of Parkinson's disease, have profound consequences on the performance of skills, as shown here for a somatosensory discrimination task. (C) 1999 Wiley-Liss, Inc

Intermanual transfer of training: blood flow correlates in the human brain

In a previous study, we found that relearning of a task with one hand might negatively be influenced by previous, opposite hand training of the analogue task, Thut G., et al., Exp. Brain Res., 108 (1996) 321-327. Drawing of a figure with the right hand, following left hand training, was slower than right hand drawing of an unknown figure. These conditions were termed right hand transfer learning (rTL) and right hand original learning (rOL). The present study aimed to identify the cerebral areas associated with these influences by measuring regional cerebral blood flow (rCBF) in 16 right-handed, healthy subjects during rTL and rOL. Positron emission tomography and statistical parametric mapping were used. Compared with rOL, rTL was associated with increased rCBF in the left medial prefrontal cortex and the right prefrontal convexity. Individual rCBF changes in the area homotopic to the right prefrontal convexity furthermore correlated with individual changes in rTL performance. While the smallest rCBF increases were found in subjects with weakest slowing of rTL relative to rOL, highest rCBF increases were present when rTL slowing dominated. Comparisons between rTL and rOL, however, revealed on average no performance differences. Our data suggest that relearning after previous opposite hand training activates neural mechanisms within the prefrontal convexity which might have an inhibitory function but that inhibition does not have to be the net final behavioral result. (C) 1997 Elsevier Science B.V

Activation of the human brain by monetary reward.

With the purpose of studying neural activation associated with reward processing in humans, we measured regional cerebral blood flow in 10 right-handed healthy subjects performing a delayed go-no go task in two different reinforcement conditions. Correct responses were either rewarded by money or a simple "ok' reinforcer. Behaviour rewarded by money, as compared with the "ok' reinforcement, was most significantly associated with activation of dorsolateral and orbital frontal cortex and also involved the midbrain and thalamus. These results may reflect the processing of reward information, although arousal effects cannot be completely excluded. It is suggested that the observed foci are implicated in the assessment of consequences in goal-directed behaviour which agrees with research in non-human primates

Impaired somatosensory discrimination of shape in Parkinson's disease:Association with caudate nucleus dopaminergic function

Tactile discrimination of macrogeometric objects in a two-alternative forced-choice procedure represents a demanding task involving somatosensory pathways and higher cognitive processing. The objects for somatosensory discrimination, i.e., rectangular parallelepipeds differing only in oblongness, were presented in sequential pairs to normal volunteers and 12 parkinsonian patients. The performance of patients was significantly impaired compared to normal volunteers. From a biochemical point of view, the patients were characterized by a severely reduced 6-[F-18]-fluoro-L-dopa (FDOPA) tracer metabolism in the basal ganglia, as measured using positron emission tomography (PET). Furthermore, reduced specific FDOPA metabolism in the putamen was consistent with the impaired motor capacities of the patients. The reduced specific FDOPA-uptake within the caudate nucleus was associated with additionally diminished somatosensory discrimination. This association, of low perception during task performance and decreased FDOPA-uptake, provides direct evidence for the role of the caudate nucleus in the cognitive part of the task. We suggest that directed attention and working memory were critically involved as a result of disturbed interactions between the head of the caudate nucleus and the dorsolateral prefrontal cortex. Furthermore, there were indications of an additional involvement of the mesolimbic system, which might be of importance during challenging situations such as forced choice. We conclude that differential effects on parts of the basal ganglia, during evolution of the degenerative process characteristic of Parkinson's disease, have profound consequences on the performance of skills, as shown here for a somatosensory discrimination task. (C) 1999 Wiley-Liss, Inc

Intermanual transfer of training:blood flow correlates in the human brain

In a previous study, we found that relearning of a task with one hand might negatively be influenced by previous, opposite hand training of the analogue task, Thut G., et al., Exp. Brain Res., 108 (1996) 321-327. Drawing of a figure with the right hand, following left hand training, was slower than right hand drawing of an unknown figure. These conditions were termed right hand transfer learning (rTL) and right hand original learning (rOL). The present study aimed to identify the cerebral areas associated with these influences by measuring regional cerebral blood flow (rCBF) in 16 right-handed, healthy subjects during rTL and rOL. Positron emission tomography and statistical parametric mapping were used. Compared with rOL, rTL was associated with increased rCBF in the left medial prefrontal cortex and the right prefrontal convexity. Individual rCBF changes in the area homotopic to the right prefrontal convexity furthermore correlated with individual changes in rTL performance. While the smallest rCBF increases were found in subjects with weakest slowing of rTL relative to rOL, highest rCBF increases were present when rTL slowing dominated. Comparisons between rTL and rOL, however, revealed on average no performance differences. Our data suggest that relearning after previous opposite hand training activates neural mechanisms within the prefrontal convexity which might have an inhibitory function but that inhibition does not have to be the net final behavioral result. (C) 1997 Elsevier Science B.V