Category learning deficits in Parkinson's disease.

Sixteen patients with Parkinson's disease (PD), 15 older controls (OCs), and 109 younger controls (YCs) were compared in 2 category-learning tasks. Participants attempted to assign colored geometric figures to 1 of 2 categories. In rule-based tasks, category membership was defined by an explicit rule that was easy to verbalize, whereas in information-integration tasks, there was no salient verbal rule and accuracy was maximized only if information from 3 stimulus components was integrated at some predecisional stage. The YCs performed the best on both tasks. The PD patients were highly impaired compared with the OCs, in the rule-based categorization task but were not different from the OCs in the information-integration task. These results support the hypothesis that learning in these 2 tasks is mediated by functionally separate systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pretraining does not ameliorate spatial learning deficits induced by intrahippocampal infusion of AP5.

Previous studies show discrepancies concerning the effects of pretraining on spatial learning deficits induced by blockade of the N-methyl-d-aspartate (NMDA) receptor. These inconsistencies might be attributed to the differences in the nature of the pretraining tasks and the method of blocking NMDA receptors. In the present study, the authors pretrained rats in a spatial water maze task. The authors then trained them with a novel spatial task in a novel environment under chronic blockade of hippocampal NMDA receptors by intrahippocampal infusion of 2-amino-5-phosphonopentanoic acid (AP5) using osmotic pumps. Although the rats had acquired the basic techniques needed to solve a water-maze spatial task during pretraining, those given high or low doses of AP5 showed acquisition deficits. As the spatial pretraining failed to ameliorate the acquisition deficits of a new task in a novel environment, it was suggested that NMDA receptors were necessary in forming spatial representations. Because neither dose of AP5 affected the performance of a spatial task in the retention phase, sensory motor disturbances could not have caused these deficits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial and object working memory deficits in Parkinson's disease are due to impairment in different underlying processes.

Working memory maintenance processes for visual-spatial and visual-object information were evaluated in patients with Parkinson's disease (PD). PD patients and controls performed a working memory task with two conditions that differed only in the aspect of the stimuli that the participant was instructed to remember: their locations or shapes. Maintenance processes were investigated by measuring accuracy over 1-s, 5-s, and 10-s delays. Results indicated that patients were impaired in maintaining object information over the delay. In contrast, the patients showed impairment on the spatial condition only when the to-be-remembered stimulus was highly similar in location to the probe, but this impairment was equivalent across the delays, suggesting that this deficit was not due to maintenance impairment. These results suggest that deficits in working memory for spatial and object information are mediated by distinct cognitive processes in nondemented patients with PD and may differ in their pathophysiological basis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of dopamine on semantic activation in Parkinson's disease: Evidence from a multipriming task.

Research has suggested that semantic processing deficits in Parkinson's disease (PD) are related to striatal dopamine deficiency. As an investigation of the influence of dopamine on semantic activation in PD, 7 participants with PD performed a lexical-decision task when on and off levodopa medication. Seven healthy controls matched to the participants with PD in terms of sex, age, and education also participated in the study. By use of a multipriming paradigm, whereby 2 prime words were presented prior to the target word, semantic priming effects were measured across stimulus onset asynchronies (SOAs) of 250 ms and 1,200 ms. The results revealed a similar pattern of priming across SOAs for the control group and the PD participants on medication. In contrast, within-group comparisons revealed that automatic semantic activation was compromised in PD participants when off medication. The implications of these results for the neuromodulatory influence of dopamine on semantic processing in PD are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Similarities and differences in spatial learning and object recognition between young male C57Bl/6J mice and Sprague-Dawley rats.

Mice and rats are often used interchangeably in neuroscience research. However, species differences in brain structure and connectivity exist within the medial temporal lobe circuits that contribute to learning and memory. The hippocampus in particular contributes to both spatial learning and recognition memory, but the extent to which rats and mice are comparable in these two cognitive domains remains unclear. To evaluate potential species differences in spatial memory and object recognition, young adult male Sprague–Dawley rats and male C57Bl/6J mice were tested in the water maze and novel object recognition tasks. Following six days of training, with four trials per day, there was no difference in the ability of rats and mice to learn the location of a hidden platform. However, rats performed better than mice on the probe trial, indicative of superior retention. In the novel object preference test, no species differences in recognition memory were detected, although rats spent more time exploring the arena and took longer to approach the objects. These observations suggest that while species differences in spatial memory retention are present, they do not correlate with differences in object recognition memory. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The risky business of dopamine agonists in Parkinson disease and impulse control disorders.

Risk-taking behavior is characterized by pursuit of reward in spite of potential negative consequences. Dopamine neurotransmission along the mesocorticolimbic pathway is a potential modulator of risk behavior. In patients with Parkinson's disease (PD), impulse control disorder (ICD) can result from dopaminergic medication use, particularly dopamine agonists (DAA). Behaviors associated with ICD include hypersexuality as well as compulsive gambling, shopping, and eating, and these behaviors are potentially linked to alterations to risk processing. Using the Balloon Analogue Risk Task, we assessed the role of agonist therapy on risk-taking behavior in PD patients with (n = 22) and without (n = 19) active ICD symptoms. Patients performed the task both “on” and “off” DAA. DAA increased risk-taking in PD patients with active ICD symptoms, but it did not affect risk behavior of PD controls. DAA dose was also important in explaining risk behavior. Both groups similarly reduced their risk-taking in high compared to low risk conditions and following the occurrence of a negative consequence, suggesting that ICD patients do not necessarily differ in their abilities to process and adjust to some aspects of negative consequences. Our findings suggest dopaminergic augmentation of risk-taking behavior as a potential contributing mechanism for the emergence of ICD in PD patients. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Implicit category learning performance predicts rate of cognitive decline in nondemented patients with Parkinson's disease.

Nondemented patients with Parkinson's disease (PD) are impaired in learning to categorize simple perceptual stimuli when category membership is defined by a nonlinear relationship between stimulus dimensions but not when the relationship is linear (J. V. Filoteo, W. T. Maddox, D. P. Salmon, & D. D. Song, 2005). In the present study, the authors examined whether performance in either of these 2 category learning conditions was predictive of global cognitive decline following a mean of 1.6 years since the time patients were 1st seen. Results indicated that final block accuracy in the nonlinear condition, but not the linear condition, predicted global cognitive decline. Performance on the Wisconsin Card Sorting Test (WCST) did not significantly predict global cognitive decline, although there was a trend for this to be the case. In addition, the association between nonlinear category learning and global cognitive decline was not impacted by patients' performance on the WCST. Results suggest that nonlinear category learning predicts cognitive decline in nondemented patients with PD and that nonlinear category learning and WCST performances may provide independent measures of integrity of the posterior and anterior caudate, respectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Beacon training in a water maze can facilitate and compete with subsequent room cue learning in rats.

In Stage 1 of 4 experiments in which rats completed a water-maze blocking procedure, experimental groups were trained to use a predictive beacon (hanging above, connected to, or displaced from the platform) to find a submerged escape platform in the presence of predictive or irrelevant background cues and in the presence or absence of irrelevant landmarks. In Stage 2, a fixed beacon, landmarks, and background cues all predicted the platform location. A Room Test (landmarks and background cues only) showed that Stage 1 training with a fixed hanging beacon or the moving displaced beacon facilitated Stage 2 learning of predictive room cues for experimental relative to control subjects. In contrast, Stage 1 training with a moving pole beacon interfered with Stage 2 learning about predictive room cues relative to controls, whereas training with a fixed pole or moving hanging beacon had no effect. We conclude that multiple spatial learning processes influence locating an escape platform in the water maze. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Explicit category learning in Parkinson's disease: Deficits related to impaired rule generation and selection processes.

The present study examined the source of explicit category learning deficits previously noted in patients with Parkinson's disease (PD). Task stimuli consisted of 4 binary-valued cues that together determined category assignment, although some cues were more important for the categorization decision. Participants verbalized the hypotheses being tested to provide several measures of the hypothesis testing. Analyses of these verbal protocols indicated that PD patients were impaired on rule generation and selection but not rule shifting. Patients had particular difficulty noting the relative importance of the cues. Specific aspects of performance were differently correlated with neuropsychological measures of working memory and hypothesis testing ability. Together, the results suggest that the cognitive processes required for explicit category learning are mediated by partially distinct neural mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extinction, renewal, and spontaneous recovery of a spatial preference in the water maze.

Four experiments with C57BL/6 mice investigated extinction of a spatial preference in the Morris water maze. In Experiment 1, a spatial preference was extinguished by exposing mice to the water maze in the absence of a platform but in the presence of the distal spatial cues. In Experiment 2, extinction occurred when the platform was removed from the pool, when it was presented in random locations, or when it was presented consistently in the opposite location. Contextual renewal (Experiment 3) and spontaneous recovery (Experiment 4) of spatial preferences argue against an interpretation of extinction in terms of unlearning and instead suggest that extinction in the water maze, like extinction in Pavlovian conditioning, suppresses the original association. Implications of these findings for theories of spatial learning and hippocampal function are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of a lateralized parietal-basal ganglia circuit in hierarchical pattern perception: Evidence from Parkinson's disease.

The role of corticostriatal circuits in hierarchical pattern perception was examined in Parkinson's disease. The hypothesis was tested that patients with right-side onset of motor symptoms (RPD, left hemisphere dysfunction) would be impaired at local level processing because the left posterior temporoparietal junction (TP) emphasizes processing of local information. By contrast, left-side onset patients (LPD; right hemisphere dysfunction) would show impaired global processing because right TP emphasizes global processing. Participants identified targets at local or global levels without and with attention biased toward those levels. Despite normal attentional control between levels, LPD patients showed a single dissociation, demonstrating abnormal global level processing under all conditions, whereas RPD patients showed abnormal local level processing mainly when attention was biased toward the local level. These findings link side of motor symptom onset to visuospatial cognitive abilities that depend upon the contralateral TP, highlighting that side of onset can predict visuospatial impairments, and provide evidence that an inferior parietal-basal ganglia pathway involving the caudate head and the hemispherically asymmetrical TP region is necessary for hierarchical pattern perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Deep brain stimulation of the subthalamic nucleus selectively improves learning of weakly associated cue combinations during probabilistic classification learning in Parkinson's disease.

Objective: Evidence from functional imaging and clinical studies on patients with Parkinson's disease (PD) or Huntington's disease (HD) suggests that the basal ganglia play a crucial role in learning on the weather prediction task (WPT). Using deep brain stimulation (DBS) on versus off methodology, the aim of this study was to investigate the effect of altering the output from the basal ganglia to the prefrontal cortex on implicit probabilistic classification learning on the WPT by patients with PD. Method: Eleven PD patients with bilateral DBS of the subthalamic nucleus (STN) and 13 matched controls completed 200 trials of the WPT on 2 separate occasions, with the patients tested with DBS of the STN on or off. Results: DBS of the STN had no effect on overall WPT learning. However, STN DBS selectively improved implicit learning of cue combinations that were weakly (implicitly), rather than strongly (explicitly), associated with the WPT outcome. Conclusions: Results suggest that the STN plays a role in implicit probabilistic classification learning by altering basal ganglia output to the frontal cortex. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The effects of cytotoxic perirhinal cortex lesions on spatial learning by rats: A comparison of the dark Agouti and Sprague-Dawley strains.

The effects of perirhinal cortex lesions in rats on spatial memory might depend on the choice of strain. The present study, therefore, compared perirhinal lesions in Sprague-Dawley rats (associated with deficits) with Dark Agouti rats (associated with null effects). Tests of reference memory and working memory in the water maze failed to provide evidence that perirhinal lesions disrupt overall levels of performance (irrespective of strain) or that these lesions have differential effects on the rates of spatial learning in these 2 strains. Strain differences were, however, found, as the Dark Agouti strain was often superior. Furthermore, the perirhinal lesions did have differential effects in the 2 strains, but these did not appear to relate directly to changes in spatial learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age-related deficits in context discrimination learning in Ts65Dn mice that model Down syndrome and Alzheimer's disease.

All individuals with Down syndrome (DS) eventually develop the neuropathology of Alzheimer's disease (AD), which is characterized by a premature loss of basal forebrain cholinergic neurons. Similarly, between 4 and 6 months of age, Ts65Dn mice, which model DS, lose cholinergic markers in their medial septal neurons. It is not known whether Ts65Dn mice have age-related learning deficits as well. Control and Ts65Dn mice were tested at several ages in context discrimination. Controls at all ages showed no deficits in learning this task. Ts65Dn mice younger than 3 months demonstrated impaired learning, suggesting a possible developmental delay in Ts65Dn mice. Four-month-old Ts65Dn mice showed no deficits, whereas Ts65Dn mice older than 5 months were impaired in learning the task. Therefore, Ts65Dn mice have an age-related learning impairment that coincides with their age-related neuroanatomical abnormalities and, consequently, may be a useful model of AD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An analysis of response, direction and place learning in an open field and T maze.

Rats were trained to locate food in a response, direction, or place problem on an open field located at 2 positions. In Experiment 1, both the response and direction groups solved the problem. The place group failed to solve the task in approximately 300 trials. Experiment 2 demonstrated that rats need distinguishable start points to solve a place problem when neither a response nor a direction solution is available. Findings from Experiment 3 suggest that a combination of path traveled and distinct cues help to differentiate start points. Experiment 4 replicated the findings using a T maze. These results suggest 'place' solutions are difficult for rats. The data are discussed with respect to conditional learning and modem spatial mapping theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of rodent hippocampus in paired-associate learning involving associations between a stimulus and a spatial location.

The ability of rats with control or hippocampal lesions to learn an object-place, odor-place, or object-odor paired-associate task was assessed in a cheeseboard maze apparatus. The data indicate that rats with hippocampal lesions were significantly impaired, compared with controls, in learning both the object-place and the odor-place paired-associate tasks. However, rats with hippocampal lesions learned the object-odor paired-associate task as readily as did controls. The data suggest that the rodent hippocampus is involved in paired-associate learning when a stimulus must be associated with a spatial location. However, the hippocampus is not involved in paired-associate learning when the association does not involve a spatial component. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning about environmental geometry: A flaw in Miller and Shettleworth's (2007) operant model.

Many studies have examined how humans and other animals reestablish a sense of direction following disorientation in enclosed environments. Results showing that geometric shape of an enclosure is typically encoded, sometimes to the exclusion of featural cues, have led to suggestions that geometry might be encoded in a dedicated geometric module. Recently, Miller and Shettleworth (2007; see record 2007-09968-001) proposed that the reorientation task be viewed as an operant task and they presented an associative operant model that appears to account for many empirical findings from reorientation studies. In this paper we show that, although Miller and Shettleworth's insights into the operant nature of the reorientation task may be sound, their mathematical model has a serious flaw. We present simulations to illustrate the implications of the flaw. We also propose that the output of a simple neural network, the perceptron, can be used to conduct operant learning within the reorientation task and can solve the problem in Miller and Shettleworth's model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term potentiation and spatial learning are associated with increased phosphorylation of TrkB and extracellular signal-regulated kinase (ERK) in the dentate gyrus: Evidence for a role for brain-derived neurotrophic factor.

In this study, the authors investigate changes in the presynaptic terminal of the dentate gyrus that accompany 2 types of hippocampal-dependent plasticity: spatial leanting and long-term potentiation (LTP). Parallel changes occurred in the dentate gyrus of rats that had undergone training in the Morris water maze and had sustained LTP. In both cases, KCl-induced brain-derived neurotrophic factor release was increased, and this was accompanied by increased phosphorylation of TrkB and the mitogen-activated protein kinase, ERK. Glutamate release was also enhanced, and the data suggest thak this may be a consequence of increased activation of TrkB and ERK. Because the data indicate that similar cellular modifications are shared by these 2 forms of plasticity, they provide circumstantial evidence that LTP satisfies some of the requirements of a memory-inducing cellular substrate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)