Error processing in normal aging and in basal ganglia disorders

Recently it has been shown that effects of aging and pathologically induced changes of basal ganglia structures may have quite similar effects on cognitive functions mediated by the medial prefrontal cortex. The question appears, if this pattern may be assignable to other cognitive functions that are mediated via the basal ganglia and medial prefrontal brain areas. Error processing is a component of executive functions that also depends on these areas and especially on the anterior cingulate cortex (ACC). Hence we ask, if error processing functions are differentially modulated by normal aging and basal ganglia diseases. Error processing mechanisms in these groups were investigated using a cognitive event-related potential (ERP), the error negativity. Enrolling an extended sample of young and elderly controls, as well as patients with Parkinson's and Huntington's disease, we show that modulations of error processing differ between aging, different basal ganglia diseases. Despite that the examined basal ganglia disorder groups (Parkinson's and Huntington's disease) differ in their age they show similar modulations in error processing, suggesting that aging effects are overridden by pathogenic effects. The study shows that it may be valuable to compare aging not only to different forms of basal ganglia disorders in order to gain knowledge about age- and disease-related mechanisms and the effects of these on cognitive functions. Diseases of the basal ganglia may impact error processing above and beyond the effects of normal aging. Although many aging, Parkinson's disease and Huntington's disease studies on error processing functions have already been published, this study ties together several related observations across all of these groups in one experiment.     

Latent Toxoplasma gondii infection leads to deficits in goal-directed behavior in healthy elderly

Goal-directed behavior is well-known to show declines in elderly individuals, possibly because of alterations in dopaminergic neural transmission. The dopaminergic system is modulated by a number of other different factors. One of these factors, which has attracted a considerable amount of interest in neurobiology, but has only rarely been examined with respect to its possible modulatory role for cognitive functions in elderly individuals, is latent Toxoplasma gondii (T. gondii) infection. Latent T. gondii infection may be of relevance to goal-directed behavior as it alters dopaminergic neural transmission. We examine goal-directed behavior in T. gondii IgG positive and negative elderly subjects in auditory distraction paradigm. We apply event-related potentials to examine which cognitive subprocesses are affected by latent T. gondii infection on a neurophysiological level. We show that latent T. gondii infection compromises the management of auditory distraction in elderly by specifically delaying processes of attentional allocation and disengagement. The results show that latent T. gondii infection is neglected but an important neurobiological modulator of cognitive functions in elderly individuals.     

Error processing--evidence from intracerebral ERP recordings

Over the last decade, several authors have described an early negative (Ne) and a later positive (Pe) potential in scalp event-related potentials (ERPs) of incorrect choice reactions. The aim of the present study was to investigate the intracerebral origin and distribution of these potentials. Seven intractable epileptic patients participated in the study. A total of 231 sites in the frontal, temporal, and parietal lobes were investigated by means of depth electrodes. A standard visual oddball paradigm was performed, and electroencephalogram (EEG) epochs with correct and incorrect motor reactions were averaged independently. Prominent, mostly biphasic, ERP complexes resembling scalp Ne/Pe potentials were consistently observed in several cortical locations after incorrect trials. The most consistent findings were obtained from mesiotemporal structures; in addition to P3-like activity found after correct responses, an Ne/Pe complex was generally detected after incorrect trials. The Pe had a longer latency than the P3. Other generators of Ne/Pe-like potentials were located in different regions of the frontal lobe. The latency of the Ne was shortest in parietal, longer in temporal, and longest in frontal regions. Our findings firstly show that multiple cortical structures generate Ne and Pe. In addition to the rostral anterior cingulate cortex, the mesiotemporal and some prefrontal cortical sites seem to represent integral components of the brain's error-checking system. Secondly, the coupling of Ne and Pe to a complex suggests a common origin of Ne and Pe. Thirdly, the latency differences of the Ne across lobes suggest that the Ne is primarily elicited in posterior and temporal, and only later in frontal regions.     

Age related strategic differences in processing irrelevant information

Deficient control of irrelevant information with greater age can be demonstrated in paradigms like inhibition of return (IOR). IOR is a mechanism to protect the organism from redirecting attention to a previously scanned irrelevant location and is assumed to be generated slower but to a comparable amount with increasing age. We investigated this putative deficit by means of event-related potentials (ERPs). As expected, IOR developed later in older subjects. In the cue-related ERPs, young subjects showed a large frontocentral N2 (reflecting control or inhibition) which was virtually absent in the old subjects. Instead, the older subjects showed a P3b, reflecting controlled processing of information. Thus, older adults process irrelevant stimuli more like relevant ones, thereby overloading their information processing system.     

The functional 5-HT1A receptor polymorphism affects response inhibition processes in a context-dependent manner

Cognitive control processes may depend on contextual information, sometimes improving performance, but impairing performance if expectancies about forthcoming events induce pre-potent responses. The neurobiological bases of these effects are not understood. Here, we examine context-dependent variations of response control processes using the AX-CPT task with respect to the relevance of the functional serotonin 1A receptor polymorphism (5-HT1A C(−1019)G) in a sample of healthy subjects (N = 90) by means of event-related potentials (ERPs).The results show that, when context information is helpful to drive behavioural performance, carriers of the −1019G allele reveal compromised cognitive control. Yet, they show enhanced task performance when strong context representations would lead to declines in behavioural control. These findings are paralleled by modulations of the (Nogo)-P3 ERP-component. These results show for the first time that, even though the −1019G allele enhances the risk to develop anxiety disorders, it also confers an advantage to its carriers in terms of better cognitive control processes in conditions where contextual information compromises cognitive control. Effects of the 5-HT1A C(−1019)G polymorphism were further modulated by anxiety sensitivity. As the functional effect of the 5-HT1A C(−1019)G polymorphism has previously been shown to be rather specific for serotonergic 1A autoreceptors in the dorsal raphe nucleus (DRN), the results suggest that contextual modulations in cognitive control may be exerted by the DRN.     

Impulsiveness and ERP components in a Go/Nogo task

Impulsiveness has been linked to fast guesses and premature responses in reaction time tasks like the Eriksen flanker task or the Go/Nogo task. In the present study, healthy subjects without history of DSM-IV Axis I or II psychopathology were examined. Impulsiveness was determined by calculating individual reaction times (as a function of general response speed) in order to split the entire group (n = 26) in a subgroup with a more controlled response style (low impulsiveness [LI] group; n = 13) and a subgroup with a more impulsive response style (high impulsiveness [HI] group; n = 13). Subjects performed a Go/Nogo task while a multi-channel EEG was recorded. Two event-related potentials (ERP) were of special interest: the Nogo-N2 and -P3 component. HI subjects had significantly reduced (less positive) Nogo-P3 amplitudes compared to LI subjects whereas groups did not differ with regard to the Nogo-N2. These results corroborate previous findings of reduced Nogo-P3 amplitudes in samples with enhanced levels of impulsiveness. Moreover, present data suggest that there is a broader range of impulsiveness even in healthy subjects which might mask or pronounce between-group differences in clinical studies. Therefore, different levels of impulsiveness in control groups should be carefully taken into account in further ERP studies.     

Electrophysiological correlates of residual switch costs

Switching among cognitive tasks results in switch costs which are only partly reduced even after sufficient task preparation. These residual switch costs are frequently explained in terms of interference of simultaneously active task representations that delays selection of a correct response. Recent studies showed that the benefit of a task- and response-set repetition can also explain residual costs. We aimed to extend the findings by clarifying the mechanisms underlying task- and response-mode repetition benefit as well as costs arising by switch of one or both dimensions. To this end we used a combination of task-switching and go/no-go paradigm during an electrophysiological recording. Particularly, we focused on the frontocentral N2, which has been usually related to conflict, but also to response selection. The behavioral results replicate previous findings of lack of residual switch costs due to slower responses in task repetitions (TRs) following no-go relative to go trials. This indicates elimination of TR benefit when in a previous trial no response was selected and prepared. In other words, task sets clearly benefits from repetition of response mode whereas interference seems to occur whenever the task-set, the response mode or both were switched. Trial incongruity increased reaction times. The event-related potentials (ERPs) revealed a frontocentral N2 in all conditions which followed the same pattern as the reaction times (RTs), showing smaller amplitude and peaking earlier when both the task and response mode were repeated relative to the three switching conditions. Similar to the behavioral data, the N2 increased as a function of incongruity. Finally, both the N2 amplitude and latency correspond closely to the residual switch costs. This finding suggests that task-set or response mode switching intensify and delay response selection, relative to the repetition of both dimensions.