Clinical asymmetry in Parkinson's disease is characterized by prevalence of subthalamic pause-burst neurons and alpha-beta oscillations.

OBJECTIVE: We aimed to establish specific biomarkers of Parkinson's disease (PD) by comparing activity of more affected (MA) and less affected (LA) subthalamic nucleus (STN) of patients with prominent clinical asymmetry. METHODS: We recorded single unit activity and local field potentials (LFP) of the STN during deep brain stimulation surgeries. Neuronal firing patterns and discharge rate, as well as oscillatory features of both single cells and LFP, were analyzed. RESULTS: We observed notable differences in proportions of irregular-burst and pause-burst, but not tonic neurons, between the hemispheres. Oscillations of pause-burst neurons correlated significantly with the bradykinesia and rigidity scores of the corresponding hemibody. LFP derived from MA STN featured greater power in 12-15 Hz. CONCLUSIONS: Our results provide evidence that the increased proportion of units with prolonged pauses may be associated with PD. We also speculate that some of them may gain rhythmicity in the alpha-beta range in relation to hypokinetic symptoms, long-term disease, or both. SIGNIFICANCE: Our findings highlight the relation between specific oscillatory features of the STN, predominance of subthalamic pause-burst units and PD pathophysiology.

Pupil dilation and response slowing distinguish deliberate explorative choices in the probabilistic learning task.

This study examined whether pupil size and response time would distinguish directed exploration from random exploration and exploitation. Eighty-nine participants performed the two-choice probabilistic learning task while their pupil size and response time were continuously recorded. Using LMM analysis, we estimated differences in the pupil size and response time between the advantageous and disadvantageous choices as a function of learning success, i.e., whether or not a participant has learned the probabilistic contingency between choices and their outcomes. We proposed that before a true value of each choice became known to a decision-maker, both advantageous and disadvantageous choices represented a random exploration of the two options with an equally uncertain outcome, whereas the same choices after learning manifested exploitation and direct exploration strategies, respectively. We found that disadvantageous choices were associated with increases both in response time and pupil size, but only after the participants had learned the choice-reward contingencies. For the pupil size, this effect was strongly amplified for those disadvantageous choices that immediately followed gains as compared to losses in the preceding choice. Pupil size modulations were evident during the behavioral choice rather than during the pretrial baseline. These findings suggest that occasional disadvantageous choices, which violate the acquired internal utility model, represent directed exploration. This exploratory strategy shifts choice priorities in favor of information seeking and its autonomic and behavioral concomitants are mainly driven by the conflict between the behavioral plan of the intended exploratory choice and its strong alternative, which has already proven to be more rewarding.

Feature binding in auditory modality requires attention as indexed by mismatch negativity and N2b in an active discrimination task.

Currently, there are two opposing views on feature binding in the auditory modality: according to behavioral studies, this process requires focused attention, whereas electrophysiological studies suggest that feature binding may be fully automatic and independent of attention. Here, we examined whether feature binding depends on higher-level attentional processes by manipulating the attentional focus. We used four auditory stimuli that differed in two features: pitch and location. Two rare deviants could be detected within a sequence of two frequent standards exclusively by feature conjunctions rather than by any single feature alone. Event-related potentials to auditory stimuli were analyzed for four conditions: selective attention to target auditory deviants, selective ignoring of nontarget auditory deviants, nonselective distributed attention to all stimuli within auditory modality, and selective attention diverted from auditory to visual modality. The negative difference (Nd) between event-related potentials to deviants and standards was measured within two time intervals, corresponding to mismatch negativity (100-200 ms) and N2b (200-300 ms). Only under the condition of selective attention to specific feature conjunctions, prominent Nd was observed in mismatch negativity as well in N2b time ranges, whereas no significant Nd was observed in other conditions. As Nd is considered a marker of deviance processing, our results support the view that deviance was not detected unless attention was focused on the stimuli, thus supporting the view that feature binding requires attention.