Jung Uk Kang

Interareal communication is crucial for coordinated brain function. Given the largely contralateral organization of the brain, bimanual coordination likely depends on interactions across the two cerebral hemispheres for motor planning and execution. The parietal reach region (PRR) is an early node in the sensorimotor transformation stream. Here, we examined the contributions of direct callosal connections between left and right PRR to bimanual coordination. Using manganese-enhanced MRI, we traced callosal pathways crossing the midline and found that PRR–PRR connections are restricted to the splenium. We then temporarily blocked these fibers with lidocaine while measuring behavioral performance and interhemispheric coherence. Blockade selectively reduced PRR–PRR coherence during bimanual movements to a common target, but not during movements to separate targets. Behaviorally, blockade sped movement initiation across tasks, consistent with a functionally inhibitory influence of interhemispheric communication, reduced the temporal synchrony of bimanual movements to a common target, and reduced errors for bimanual movements to separate targets. These findings provide causal evidence that posterior callosal communication supports the temporal precision of spatially coordinated bimanual actions, while potentially constraining independent limb control.

Inhibitory control has been associated with the right inferior frontal cortex, supported by converging evidence from lesion, stimulation, and neuroimaging studies. Recent work, however, emphasizes the role of distributed cortical networks for inhibitory control. Eggert et al. (2025) used source-resolved electroencephalogram and directed connectivity analyses to characterize large-scale cortical interactions during response inhibition, identifying the anterior insula as a coordinating node. Here, we situate these findings within the broader literature spanning electroencephalogram, functional magnetic resonance imaging, and human intracranial electrophysiology. Electroencephalogram connectivity analyses complement existing work by characterizing large-scale coordination, particularly given the challenges of dissociating inferior frontal cortex and anterior insula. When considered alongside causal and intracranial evidence, these results support inhibitory control as an emergent property of distributed cortical systems.

Inter-areal communication is crucial for brain function. Given the largely contralateral organization of the brain, bimanual coordination likely involves interactions across the two cerebral hemispheres for motor planning and execution. The parietal reach region (PRR) is an early node in the sensorimotor transformation stream. Here we examine the contributions of direct callosal connections between left and right PRR to bimanual coordination. Using manganese-enhanced magnetic resonance imaging, we traced callosal pathways crossing the midline and found that PRR-PRR connections are restricted to the splenium. We then temporarily blocked these fibers with lidocaine while measuring behavioral performance and interhemispheric coherence. Blockade reduced task-specific PRR-PRR coherence during bimanual movements. Behaviorally, blockade sped movement initiation across tasks, consistent with an inhibitory role of interhemispheric communication, reduced the temporal synchrony of bimanual movements to a common target and reduced errors for bimanual movements to separate targets. These findings provide causal evidence that posterior callosal communication supports spatial coordination of bimanual actions but may also constrain independent limb control. Significance Statement Classic split-brain studies revealed that severing the corpus callosum impairs bimanual coordination, but the specific pathways and mechanisms remain unclear. In macaques, we transiently disrupted the posterior corpus callosum connecting left and right parietal reach regions (PRR), which encode planned contralateral arm movements. This targeted blockade reduced task-specific neural synchrony between PRRs and selectively impaired coordination when both arms reached to a common target, while improving performance when the arms moved to separate targets. Movement initiation was also sped up across tasks, consistent with an inhibitory role of interhemispheric communication. These findings provide causal evidence that posterior callosal communication enables spatially coordinated bimanual movements, extending foundational split-brain insights to defined cortical circuits in a non-human primate model.

The ability to override prepotent actions is critical to control impulses and adjust behavior depending on goals and contextual needs. In this study, we investigate the inhibitory control abilities of a patient diagnosed with Klüver-Bucy Syndrome following a left temporal resection. The patient presented with disruptive hypersexuality symptoms akin to compulsions, leading to the inability to control and suppress inappropriate actions. The patient was recruited for the current research study while undergoing intracranial monitoring for epilepsy, to investigate the cognitive and neural processes underlying the patient’s inhibitory control symptoms. We formulated the hypothesis that an inhibitory control deficit emerges in response to provocative triggers, and we designed a personalized paradigm pairing arousing images with a classic inhibitory control task. We not only confirmed disrupted performance following exposure to triggering, provocative material, but we also leveraged the simultaneously recorded neural data to identify a biomarker reflecting inhibitory control failures. Next, we repeated the experimental paradigm during and after personalized neuromodulation via direct high-frequency stimulation of the right inferior frontal cortex. The patient displayed a marked improvement in his behavior during neuromodulation, mirrored by changes in neural activity, spanning spectral features, event-related potentials and functional connectivity. Altogether, our study revealed that the patient’s symptoms were not due to a global inhibition deficit, but to a specific control issue triggered by exposure to provocative material. Overall, our work showcases a feasible, effective approach towards data-driven personalized neuromodulation, which could be leveraged to mitigate specific inhibitory control deficits and potentially other symptoms of executive dysfunction. Abstract Figure: Graphical abstract. This case study investigates context-dependent inhibitory control abilities in a patient with Kluver-Bucy syndrome during intracranial monitoring for epilepsy .

Summary: Recent evidence indicates that the intraparietal sulcus (IPS) may play a causal role in action stopping, potentially representing a novel neuromodulation target for inhibitory control dysfunctions. Here, we leverage intracranial recordings in human subjects to establish the timing and directionality of information flow between IPS and prefrontal and cingulate regions during action stopping. Prior to successful inhibition, information flows primarily from the inferior frontal gyrus (IFG), a critical inhibitory control node, to IPS. In contrast, during stopping errors the communication between IPS and IFG is lacking, and IPS is engaged by posterior cingulate cortex, an area outside of the classical inhibition network and typically associated with default mode. Anterior cingulate and orbitofrontal cortex also display performance-dependent connectivity with IPS. Our functional connectivity results provide direct electrophysiological evidence that IPS is recruited by frontal and anterior cingulate areas to support action plan monitoring/updating, and by posterior cingulate during control failures. In brief: Functional connectivity between the intraparietal sulcus (IPS) and a set of frontal and cingulate regions indicates that IPS is recruited to aid inhibitory control. Control failures are associated with increased communication with posterior cingulate. IPS could be a novel and tractable neuromodulation target for control-related neuropsychiatric disorders. Highlights: Parietal cortex displays performance-dependent activity in action stopping Functional connectivity between IPS and IFG underlies successful stopping Early communication from ACC and OFC to IPS is also specific to successful stopping Communication from PCC to IPS is higher during lapses in control

Visual processing in the brain has been understood as the ventral and dorsal pathways processing “what” and “where” information, respectively. Mocz et al. (Mocz V, Vaziri-Pashkam M, Chun M, Xu Y. J Cogn Neurosci 34: 2406–2435, 2022), however, report that the two pathways code object features in a parallel manner. These results support that information processing in the dorsal pathway is not strictly limited to “where” and that the two pathways work in parallel to process task-relevant information (“what we do with it”).