Christian Bellebaum

Cerebellar involvement in executive control.

The cerebellum has long been considered to be mainly involved in motor function. In the last 20 years, evidence from neuroimaging studies and from investigations of patients with cerebellar lesions has shown that the cerebellum plays a role in a range of cognitive functions. While cerebellar contributions have been shown for learning and memory, the cerebellum has also been linked to higher order cognitive control processes frequently referred to as executive functions. Although it is widely accepted that the cerebellum contributes to cognitive processing, the nature of cerebellar involvement is not well understood. The present paper focuses on the role of the cerebellum in executive processing, reviewing findings derived from neuroimaging studies or from studies investigating deficits related to cerebellar dysfunction. As executive functions cannot be considered as a unitary concept, special emphasis is put on cerebellar contributions to different aspects of executive control such as working memory, multitasking or inhibition. Referring to models derived from motor control, possible mechanisms of cerebellar involvement in executive processing are discussed. Finally, methodological problems in assessing executive deficits in general and in assessing the cerebellar contribution to executive processing in particular are addressed.

It is less than you expected: The feedback-related negativity reflects violations of reward magnitude expectations

The anterior cingulate cortex (ACC) is involved in performance monitoring and in learning from performance feedback. Recent research suggests that the feedback-related negativity (FRN), an event-related potentials (ERP) component reflecting neural activity in the ACC, codes the size of a negative prediction error when reward probabilities are varied. There is as yet no clear evidence that the FRN is also sensitive to violations of reward magnitude expectations. In the present study, 20 healthy young subjects engaged in a learning task in which a coin had to be found on each trial. The value of the coin (the potential reward magnitude) was varied from trial to trial and amounted to 5 cent, 20 cent or 50 cent. Analysis of ERPs revealed that FRN amplitude differences between reward and non-reward were significantly modulated by (potential) reward magnitude. This effect was driven by the neural response to non-reward: the larger the potential reward, the larger was the FRN amplitude in response to non-reward. In contrast, the P300 was larger for positive outcomes and showed an effect of (potential) reward magnitude independent of valence. Together with evidence from previous studies, these results show that the FRN codes negative prediction errors in the context of varying reward probabilities and magnitudes. The findings are in line with recent results based on functional neuroimaging and lend further support to the idea of a key role of the ACC in the integration of information on different aspects of performance outcomes.

Cognitive deficits in narcolepsy.

The aim of the investigations was to explore the nature and the severity of cognitive deficits in narcolepsy patients. In two studies, narcolepsy patients were compared with matched control subjects on a range of attention, memory and executive control tasks. Impairments were only observed on attention and executive function tasks which involved higher demands on inhibition or task management abilities whereas relatively routine memory and attention tasks yielded intact performance in narcolepsy patients. The overall pattern of results indicates an executive control deficit in narcolepsy which might be related to a reduction of available cognitive processing resources because of the need for continuous allocation of resources to monitoring and maintenance of vigilance.

Focal basal ganglia lesions are associated with impairments in reward-based reversal learning

The basal ganglia (BG) are thought to play a key role in learning from feedback, with mesencephalic dopamine neurons coding errors in reward prediction, thereby mediating information processing in the BG and the prefrontal cortex. In the present study, reward-based learning was assessed in patients with focal BG lesions, by studying outcome-based acquisition and reversal of stimulus-stimulus associations with different reward magnitudes in two probabilistic learning tasks. Eleven patients with selective BG lesions (three females) and 18 healthy control subjects (six females) participated in this study. Two cognitive transfer tasks provided a measure of declarative learning strategy application. On the group level, BG patients showed deficits in reversal learning, with dorsal striatum lesion patients being most severely affected. While basic mechanisms of learning from feedback such as the processing of different reward magnitudes appeared to be intact, patients needed more trials than controls to learn a second reward-based task, suggesting reduced carry-over effects in learning. A patient with a bilateral BG lesion showed better performance than controls on most learning tasks, applying a compensatory declarative learning strategy. The results are discussed in terms of the implication of different BG subregions in different aspects of learning from feedback.

Clipping versus coiling: neuropsychological follow up after aneurysmal subarachnoid haemorrhage (SAH).

ABSTRACT Patients treated with microsurgical clipping of ruptured intracranial aneurysms often suffer from neuropsychological deficits in spite of a good neurological outcome. The purpose of this study was to explore if the deficits are related to the type of therapy. Two groups of 16 patients each suffering from aneurysmal SAH, matched for sex, age, aneurysm-site and Hunt and Hess score, and 16 control subjects were examined with a battery of neuropsychological tests including memory, attention, and executive function. Depression, mood, and quality of life were also assessed. One patient group had been treated with surgical clipping, the other with endovascular coiling. Both patient groups showed deficits in verbal and visual memory. Clipped patients were slightly more impaired than coiled patients, especially on measures of affect and on a self-assessment measure of executive function. The pattern of results suggests that the neuropsychological outcome after aneurysmal SAH is affected by both the severity of the bleeding and the type of therapy.

It Was Not MY Fault: Event-Related Brain Potentials in Active and Observational Learning from Feedback

Performance feedback during learning is accompanied by a negative event-related potentials (ERP) component, the feedback-related negativity (FRN), which codes a reward prediction error. An open issue relates to the coding of feedback stimuli in observational learning. The present study aimed to determine differences in the neural processing of feedback in active and observational learners in a between-subjects design. By choosing between different stimuli, 15 active learners could learn a rule determining the probability of monetary reward. Each of the 15 observers was yoked to the performance of one active learner. In test trials, observers could prove whether they had gained insight into the rule. Although both groups learned at a comparable rate, FRN amplitudes following negative feedback were significantly reduced in observational relative to active learners, whereas there was no difference for the FRN in response to positive feedback. Additionally, between-group differences were already observed in the time window preceding the FRN, between 150 and 220 ms after feedback onset. The processing of feedback stimuli thus depends upon the direct relevance for ones own action planning. The FRN as an error signal indicating the need for behavioral adaptation appears to be especially relevant, if negative feedback is linked to agency.

The Cerebellum Is Involved in Reward-based Reversal Learning

The cerebellum has recently been discussed in terms of a possible involvement in reward-based associative learning. To clarify the cerebellar contribution, eight patients with focal vascular lesions of the cerebellum and a group of 24 healthy subjects matched for age and IQ were compared on a range of different probabilistic outcome-based associative learning tasks, assessing acquisition, reversal, cognitive transfer, and generalization as well as the effect of reward magnitude. Cerebellar patients showed intact acquisition of stimulus contingencies, while reward-based reversal learning was significantly impaired. In addition, the patients showed slower acquisition of new stimulus contingencies in a second reward-based learning task, which might reflect reduced carry-over effects. Reward magnitude affected learning only during initial acquisition, with better learning on trials with high rewards in patients and control subjects. Overall, the findings suggest that the cerebellum is implicated in reversal learning as a dissociable component of reward-based learning.

Aging affects acquisition and reversal of reward-based associative learning.

Reward-based associative learning is mediated by a distributed network of brain regions that are dependent on the dopaminergic system. Age-related changes in key regions of this system, the striatum and the prefrontal cortex, may adversely affect the ability to use reward information for the guidance of behavior. The present study investigated the effects of healthy aging on different components of reward learning, such as acquisition, reversal, effects of reward magnitude, and transfer of learning. A group of 30 young (mean age = 24.2 yr) and a group of 30 older subjects (mean age = 64.1 yr) completed two probabilistic reward-based stimulus association learning tasks. Older subjects showed poorer overall acquisition and impaired reversal learning, as well as deficits in transfer learning. When only those subjects who showed evidence of significant learning were considered, younger subjects showed equivalently fast learning irrespective of reward magnitude, while learning curves in older subjects were steeper for high compared to low reward magnitudes. Acquired equivalence learning, which requires generalization across stimuli and transfer of learned contingencies to new stimuli, was mildly impaired in older subjects.

Impairment of probabilistic reward-based learning in schizophrenia.

Recent models assume that some symptoms of schizophrenia originate from defective reward processing mechanisms. Understanding the precise nature of reward-based learning impairments might thus make an important contribution to the understanding of schizophrenia and the development of treatment strategies. The present study investigated several features of probabilistic reward-based stimulus association learning, namely the acquisition of initial contingencies, reversal learning, generalization abilities, and the effects of reward magnitude. Compared to healthy controls, individuals with schizophrenia exhibited attenuated overall performance during acquisition, whereas learning rates across blocks were similar to the rates of controls. On the group level, persons with schizophrenia were, however, unable to learn the reversal of the initial reward contingencies. Exploratory analysis of only the subgroup of individuals with schizophrenia who showed significant learning during acquisition yielded deficits in reversal learning with low reward magnitudes only. There was further evidence of a mild generalization impairment of the persons with schizophrenia in an acquired equivalence task. In summary, although there was evidence of intact basic processing of reward magnitudes, individuals with schizophrenia were impaired at using this feedback for the adaptive guidance of behavior.

Altered Error Processing following Vascular Thalamic Damage: Evidence from an Antisaccade Task

Event-related potentials (ERP) research has identified a negative deflection within about 100 to 150 ms after an erroneous response – the error-related negativity (ERN) - as a correlate of awareness-independent error processing. The short latency suggests an internal error monitoring system acting rapidly based on central information such as an efference copy signal. Studies on monkeys and humans have identified the thalamus as an important relay station for efference copy signals of ongoing saccades. The present study investigated error processing on an antisaccade task with ERPs in six patients with focal vascular damage to the thalamus and 28 control subjects. ERN amplitudes were significantly reduced in the patients, with the strongest ERN attenuation being observed in two patients with right mediodorsal and ventrolateral and bilateral ventrolateral damage, respectively. Although the number of errors was significantly higher in the thalamic lesion patients, the degree of ERN attenuation did not correlate with the error rate in the patients. The present data underline the role of the thalamus for the online monitoring of saccadic eye movements, albeit not providing unequivocal evidence in favour of an exclusive role of a particular thalamic site being involved in performance monitoring. By relaying saccade-related efference copy signals, the thalamus appears to enable fast error processing. Furthermore early error processing based on internal information may contribute to error awareness which was reduced in the patients.