A hypothetical role of cortico-basal ganglia-thalamocortical loops in visual processing

Neurophysiological mechanisms of circadian cognitive control in RLS patients - an EEG source localization study

The circadian variation of sensory and motor symptoms with increasing severity in the evening and at night is a key diagnostic feature/symptom of the restless legs syndrome (RLS). Even though many neurological diseases have shown a strong nexus between motor and cognitive symptoms, it has remained unclear whether cognitive performance of RLS patients declines in the evening and which neurophysiological mechanisms are affected by the circadian variation. In the current study, we examined daytime effects (morning vs. evening) on cognitive performance in RLS patients (n = 33) compared to healthy controls (n = 29) by analyzing flanker interference effects in combination with EEG and source localization techniques. RLS patients showed larger flanker interference effects in the evening than in the morning (p = .023), while healthy controls did not display a comparable circadian variation. In line with this, the neurophysiological data showed smaller N1 amplitudes in RLS patients compared to controls in the interfering task condition in the evening (p = .042), but not in the morning. The results demonstrate diurnal cognitive changes in RLS patients with intensified impairments in the evening. It seems that not all dopamine-regulated cognitive processes are altered in RLS and thus show daytime-dependent impairments. Instead, the daytime-related cognitive impairment emerges from attentional selection processes within the extra-striate visual cortex, but not from later cognitive processes such as conflict monitoring and response selection.

•

RLS patients have larger flanker interference effect in the evening.

•

RLS patients have enhanced impairment of attentional selection in the evening.

•

Nocturnal attentional impairment relies on the extra-striate visual cortex.

•

Conflict monitoring and response selection are not affected by RLS.

How may the basal ganglia contribute to auditory categorization and speech perception?

Listeners must accomplish two complementary perceptual feats in extracting a message from speech. They must discriminate linguistically-relevant acoustic variability and generalize across irrelevant variability. Said another way, they must categorize speech. Since the mapping of acoustic variability is language-specific, these categories must be learned from experience. Thus, understanding how, in general, the auditory system acquires and represents categories can inform us about the toolbox of mechanisms available to speech perception. This perspective invites consideration of findings from cognitive neuroscience literatures outside of the speech domain as a means of constraining models of speech perception. Although neurobiological models of speech perception have mainly focused on cerebral cortex, research outside the speech domain is consistent with the possibility of significant subcortical contributions in category learning. Here, we review the functional role of one such structure, the basal ganglia. We examine research from animal electrophysiology, human neuroimaging, and behavior to consider characteristics of basal ganglia processing that may be advantageous for speech category learning. We also present emerging evidence for a direct role for basal ganglia in learning auditory categories in a complex, naturalistic task intended to model the incidental manner in which speech categories are acquired. To conclude, we highlight new research questions that arise in incorporating the broader neuroscience research literature in modeling speech perception, and suggest how understanding contributions of the basal ganglia can inform attempts to optimize training protocols for learning non-native speech categories in adulthood.

An attractor-based complexity measurement for Boolean recurrent neural networks

We provide a novel refined attractor-based complexity measurement for Boolean recurrent neural networks that represents an assessment of their computational power in terms of the significance of their attractor dynamics. This complexity measurement is achieved by first proving a computational equivalence between Boolean recurrent neural networks and some specific class of -automata, and then translating the most refined classification of -automata to the Boolean neural network context. As a result, a hierarchical classification of Boolean neural networks based on their attractive dynamics is obtained, thus providing a novel refined attractor-based complexity measurement for Boolean recurrent neural networks. These results provide new theoretical insights to the computational and dynamical capabilities of neural networks according to their attractive potentialities. An application of our findings is illustrated by the analysis of the dynamics of a simplified model of the basal ganglia-thalamocortical network simulated by a Boolean recurrent neural network. This example shows the significance of measuring network complexity, and how our results bear new founding elements for the understanding of the complexity of real brain circuits.

Relation of Parkinson's disease subtypes to visual activities of daily living

Visual perceptual problems are common in Parkinson's disease (PD) and often affect activities of daily living (ADLs). PD patients with non-tremor symptoms at disease onset (i.e., rigidity, bradykinesia, gait disturbance or postural instability) have more diffuse neurobiological abnormalities and report worse non-motor symptoms and functional changes than patients whose initial symptom is tremor, but the relation of motor symptom subtype to perceptual deficits remains unstudied. We assessed visual ADLs with the Visual Activities Questionnaire in 25 non-demented patients with PD, 13 with tremor as the initial symptom and 12 with an initial symptom other than tremor, as well as in 23 healthy control participants (NC). As expected, the non-tremor patients, but not the tremor patients, reported more impairment in visual ADLs than the NC group, including in light/dark adaptation, acuity/spatial vision, depth perception, peripheral vision and visual processing speed. Non-tremor patients were significantly worse than tremor patients overall and on light/dark adaptation and depth perception. Environmental enhancements especially targeted to patients with the non-tremor PD subtype may help to ameliorate their functional disability.

Variations in the TNF-α Gene (TNF-α -308G→A) Affect Attention and Action Selection Mechanisms in a Dissociated Fashion

There is growing interest to understand the molecular basis of complex cognitive processes. While neurotransmitter systems have frequently been examined, other, for example neuroimmunological factors have attracted much less interest. Recent evidence suggests that the A allele of the tumor necrosis factor alpha (TNF-α) 308G→A single nucleotide polymorphism (SNP; rs1800629) enhances cognitive functions. However, it is also known that TNF-α exerts divergent, region-specific effects on neuronal functioning. Thus the finding that the A allele is associated with enhanced cognitive performance may be due to regionally specific effects of TNF-α. In this study, associations between the TNF-α −308G→A single nucleotide polymorphism (rs1800629) and cognitive function in an event-related potential (ERP) study in healthy participants ( n = 96) are investigated. We focus on subprocesses of stimulus-response compatibility that are known to be mediated by different brain systems. The results show a dissociative effect of the TNF- 308G→A SNP on ERPs reflecting attentional (N1) versus conflict and action selection processes [N2 and early-lateralized readiness potential (e-LRP)] between the AA/AG and the GG genotypes. Compared with the GG genotype group, attentional processes (N1) were enhanced in the combined AA/AG genotype group, while conflict processing functions (N2) and the selection of actions (LRP) were reduced. The results refine the picture of the effects of the TNF-α −308G→A SNP on cognitive functions and emphasize the known divergent effects of TNF-α on brain functions.

Stimulus-Response Compatibility in Huntington's Disease: A Cognitive-Neurophysiological Analysis

The basal ganglia are assumed to be of importance in action/response selection, but results regarding the importance are contradictive. We investigate these processes in relation to attentional processing using event-related potentials (ERPs) in Huntington's disease (HD), an autosomal genetic disorder expressed by degeneration of the basal ganglia, using a flanker task. A symptomatic HD group, a presymptomatic HD group (pHD), and healthy controls were examined. In the behavioral data, we found a general response slowing in HD while the compatibility effect was the same for all groups. The ERP data show a decrease of the N1 on the flanker in HD and pHD; this suggests deficient attentional processes. The N1 on the target was unaffected, suggesting that the attentional system in HD is not entirely deficient. The early lateralized readiness potential (LRP), reflecting automatic response activation due to the flankers, was unchanged, whereas the late LRP, reflecting controlled response selection due to the target information, was delayed in HD. Thus levels of action-selection processes are differentially affected in HD with automatic processes seeming to be more robust against neurodegeneration. The N2, usually associated with conflict processing, was reduced in the HD but not in the pHD and the control groups. Because the N2 was related to the LRP and reaction times in all groups, the N2 may generally not be related to conflict but rather to controlled response selection, which is impaired in HD. Overall, the results suggest alterations in attentional control, conflict processing, and controlled response selection in HD but not in automatic response selection.