Secondary motor areas for response inhibition: an epicortical recording and stimulation study

Hierarchical Organization of Bilateral Prefrontal-Basal Ganglia Circuits for Response Inhibition Control

Response inhibition control is primarily supported by the right inferior frontal gyrus (IFG) and the prefrontal-basal ganglia network, though the mechanisms behind right lateralization and regional interplay remain unclear. In this fMRI study, we explore the neural substrates supporting efficient inhibition control and examine whether the typical right lateralization of IFG activation can be modulated by stimulus properties (semantic features) and inhibitory demand (reaction times, RT). We chose a Go/No-Go lexical decision task, utilizing concrete and abstract words as Go stimuli and pseudo-word as No-Go stimuli. Behavioral results reveal that inhibition is more effective during concrete word sessions compared to abstract word sessions, suggesting a modulation of cognitive inhibition by semantic features. Neuroimaging results further demonstrate that successful inhibition activates bilateral IFG, indicating a flexible right lateralization pattern of IFG activation that varies with stimulus properties. To examine how varying inhibitory demands modulate neural activation patterns, we reclassified concrete and abstract sessions into fast and slow sessions based on RT, followed by within-group comparisons. Our study highlights the crucial role of the bilateral subthalamic nucleus (STN) in efficient inhibition, with increased activation associated with rapid response inhibition. Furthermore, we report enhanced neural coupling between the right IFG and multiple functionally connected regions, including bilateral insula, putamen, and pallidum, as well as between the right middle frontal gyrus and other prefrontal regions during rapid inhibitory responses, whereas no engagement of the left IFG was observed in efficient inhibition. These findings imply a hierarchical functional organization of the bilateral fronto-basal ganglia circuits, in which the right prefrontal regions play a dominant role in inhibition control, supported by basal ganglia regions, while the left IFG may serve a supplementary function. Stimulus properties can modulate right lateralization, underscoring the dynamic and flexible nature of the prefrontal-basal ganglia network in inhibition control.

Role of the premotor and the precentral negative motor area in praxis: A direct electrical stimulation study with behavioral analysis

OBJECTIVE

Although the negative motor area (NMA) is defined as the area where electrical cortical stimulation inhibits voluntary movements, detail functions of NMA on praxis have not been elucidated. We investigated its role in praxis by motion analysis during stimulation at a smaller intensity.

METHODS

Patients were six intractable partial epilepsy patients undergoing implantation of intracranial electrodes. Motion impairments by stimulation were studied in finger tapping, reach-to-grasp, finger gesture, and pantomime of tool use.

RESULTS

NMAs were identified on the precentral gyrus (4 patients), ventral premotor area (1), and at their border (1). In patients with precentral NMA, quantitative analysis revealed decreased tapping stroke and grasping aperture, while reaching velocity and pantomime did not change. As for more rostral NMA, quantitative stroke, aperture, and reaching velocity were decreased. One patient showed the arrest of finger gestures and pantomime, and the other had prolongation of reaction time. These two NMAs showed distinct connectivity pattern in connectivity analysis.

CONCLUSIONS

Precentral NMA seemed to play a role in elementary finger movement control, whereas more rostral NMA in complex movement. The findings indicate functional differences within NMAs.

SIGNIFICANCE

These findings elucidated the contribution of the human premotor area to the highly skilled hand movements.

Patterns of brain activity in choice or instructed go and no-go tasks

The goal of this study was to investigate the decision making process for choosing what movements to make. We used electroencephalography (EEG) to investigate patterns of the contingent negative variation (CNV) associated with free-choice decisions to move or abstain, comparing them to conditions where actions were commanded. Our primary hypothesis was that choice tasks would differ significantly from each other and exhibit EEG patterns akin to their command-driven counterparts after the decisions were made, at least, in the 50 ms block of time prior to movement. A secondary analysis evaluated post hoc comparisons of time, in 50 ms blocks, to understand the temporal development of the CNV for each condition. We also conducted an exploratory analysis of EEG event-related desynchronization (ERD) to identify patterns of brain activity associated with the decision-making process. This approach was taken due to the exploratory nature of our hypotheses concerning the spatial and temporal characteristics of EEG activity during these free-choice versus commanded tasks. We studied 12 right-handed healthy volunteers (7 women, mean age 53 years, range 39-73 years) with no prior history of neurological or major psychiatric illness. A CNV paradigm encompassing commanded and choice tasks was devised, with a 2500 ms interval between S1 and S2, while recording EEG and electromyography (EMG). S1 provided full information about the upcoming task, which was to be executed at the time of S2. We assessed CNV and explored whole scalp EEG activity, including both voltage as well as power in the alpha and beta frequency ranges. Clear and similar CNVs were observed for command and choice go tasks prior to the movements, contrasting with near-zero CNVs for the command and choice no-go tasks. Separation of CNVs for command go and no-go tasks occurred around 1600 ms post-S1, and choice CNVs separated about 2150 ms post-S1. Exploratory analysis revealed that beta power provided information about decision and preparation processes much earlier. The left dorsolateral prefrontal cortex (DLPFC) exhibited the initial sign of decision approximately 500 ms post-S1 for all tasks, with subsequent preparation for movement or restraint involving distinct activity in various brain regions. The localization of effects in the left DLPFC was determined by visual analysis of the informative electrode sites. The CNVs separate about 2 s after S1, and it appears that this process represents preparation for movement (or no movement). Exploration of the beta activity suggests an earlier decision process which leads eventually to subsequent task preparation and activation. Choice decisions lag slightly behind command decisions, with the CNV apparently reflecting motor implementation rather than the decision-making process. In a simple motor task with an exploratory analysis, both commanded and choice-based decisions are rapidly initiated in the left DLPFC. While the CNV distinguishes between go and no-go conditions, it primarily appears to signify preparation for implementation of the task following the earlier decision. Further controlled studies will be needed to confirm these results.