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1. Bihemispheric network dynamics coordinating vocal feedback control

   https://doi.org/10.1002/hbm.23114  

   Kort, Naomi S. ; Cuesta, Pablo ; Houde, John F. ; Nagarajan, Srikantan S. ( February 2016 , Human Brain Mapping)

   Modulation of vocal pitch is a key speech feature that conveys important linguistic and affective information. Auditory feedback is used to monitor and maintain pitch. We examined induced neural high gamma power (HGP) (65–150 Hz) using magnetoencephalography during pitch feedback control. Participants phonated into a microphone while hearing their auditory feedback through headphones. During each phonation, a single real‐time 400 ms pitch shift was applied to the auditory feedback. Participants compensated by rapidly changing their pitch to oppose the pitch shifts. This behavioral change required coordination of the neural speech motor control network, including integration of auditory and somatosensory feedback to initiate change in motor plans. We found increases in HGP across both hemispheres within 200 ms of pitch shifts, covering left sensory and right premotor, parietal, temporal, and frontal regions, involved in sensory detection and processing of the pitch shift. Later responses to pitch shifts (200–300 ms) were right dominant, in parietal, frontal, and temporal regions. Timing of activity in these regions indicates their role in coordinating motor change and detecting and processing of the sensory consequences of this change. Subtracting out cortical responses during passive listening to recordings of the phonations isolated HGP increases specific to speech production, highlighting right parietal and premotor cortex, and left posterior temporal cortex involvement in the motor response. Correlation of HGP with behavioral compensation demonstrated right frontal region involvement in modulating participant's compensatory response. This study highlights the bihemispheric sensorimotor cortical network involvement in auditory feedback‐based control of vocal pitch.Hum Brain Mapp 37:1474‐1485, 2016. © 2016 Wiley Periodicals, Inc.

    

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2. High‐definition transcranial direct current stimulation dissociates fronto‐visual theta lateralization during visual selective attention

   https://doi.org/10.1113/JP278788  

   Spooner, Rachel K. ; Eastman, Jacob A. ; Rezich, Michael T. ; Wilson, Tony W. ( February 2020 , The Journal of Physiology)

   Visual attention involves discrete multispectral oscillatory responses in visual and ‘higher‐order’ prefrontal cortices.

   Prefrontal cortex laterality effects during visual selective attention are poorly characterized.

   High‐definition transcranial direct current stimulation dynamically modulated right‐lateralized fronto‐visual theta oscillations compared to those observed in left fronto‐visual pathways.

   Increased connectivity in right fronto‐visual networks after stimulation of the left dorsolateral prefrontal cortex resulted in faster task performance in the context of distractors.

   Our findings show clear laterality effects in theta oscillatory activity along prefrontal–visual cortical pathways during visual selective attention.

   Studies of visual attention have implicated oscillatory activity in the recognition, protection and temporal organization of attended representations in visual cortices. These studies have also shown that higher‐order regions such as the prefrontal cortex are critical to attentional processing, but far less is understood regarding prefrontal laterality differences in attention processing. To examine this, we selectively applied high‐definition transcranial direct current stimulation (HD‐tDCS) to the left or right dorsolateral prefrontal cortex (DLPFC). We predicted that HD‐tDCS of the leftversusright prefrontal cortex would differentially modulate performance on a visual selective attention task, and alter the underlying oscillatory network dynamics. Our randomized crossover design included 27 healthy adults that underwent three separate sessions of HD‐tDCS (sham, left DLPFC and right DLPFC) for 20 min. Following stimulation, participants completed an attention protocol during magnetoencephalography. The resulting oscillatory dynamics were imaged using beamforming, and peak task‐related neural activity was subjected to dynamic functional connectivity analyses to evaluate the impact of stimulation site (i.e. left and right DLPFC) on neural interactions. Our results indicated that HD‐tDCS over the left DLPFC differentially modulated right fronto‐visual functional connectivity within the theta band compared to HD‐tDCS of the right DLPFC and further, specifically modulated the oscillatory response for detecting targets among an array of distractors. Importantly, these findings provide network‐specific insight into the complex oscillatory mechanisms serving visual selective attention.

    

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3. Neural Interactions Underlying Visuomotor Associations in the Human Brain

   https://doi.org/10.1093/cercor/bhy333  

   Madhavan, Radhika ; Bansal, Arjun K. ; Madsen, Joseph R. ; Golby, Alexandra J. ; Tierney, Travis S. ; Eskandar, Emad N. ; Anderson, William S. ; Kreiman, Gabriel ( December 2018 , Cerebral Cortex)

   Rapid and flexible learning during behavioral choices is critical to our daily endeavors and constitutes a hallmark of dynamic reasoning. An important paradigm to examine flexible behavior involves learning new arbitrary associations mapping visual inputs to motor outputs. We conjectured that visuomotor rules are instantiated by translating visual signals into actions through dynamic interactions between visual, frontal and motor cortex. We evaluated the neural representation of such visuomotor rules by performing intracranial field potential recordings in epilepsy subjects during a rule-learning delayed match-to-behavior task. Learning new visuomotor mappings led to the emergence of specific responses associating visual signals with motor outputs in 3 anatomical clusters in frontal, anteroventral temporal and posterior parietal cortex. After learning, mapping selective signals during the delay period showed interactions with visual and motor signals. These observations provide initial steps towards elucidating the dynamic circuits underlying flexible behavior and how communication between subregions of frontal, temporal, and parietal cortex leads to rapid learning of task-relevant choices.

    

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4. Distinct neural representations during a brain–machine interface and manual reaching task in motor cortex, prefrontal cortex, and striatum

   https://doi.org/10.1038/s41598-023-44405-y  

   Zippi, Ellen L. ; Shvartsman, Gabrielle F. ; Vendrell-Llopis, Nuria ; Wallis, Joni D. ; Carmena, Jose M. ( October 2023 , Scientific Reports)

   Although brain–machine interfaces (BMIs) are directly controlled by the modulation of a select local population of neurons, distributed networks consisting of cortical and subcortical areas have been implicated in learning and maintaining control. Previous work in rodents has demonstrated the involvement of the striatum in BMI learning. However, the prefrontal cortex has been largely ignored when studying motor BMI control despite its role in action planning, action selection, and learning abstract tasks. Here, we compare local field potentials simultaneously recorded from primary motor cortex (M1), dorsolateral prefrontal cortex (DLPFC), and the caudate nucleus of the striatum (Cd) while nonhuman primates perform a two-dimensional, self-initiated, center-out task under BMI control and manual control. Our results demonstrate the presence of distinct neural representations for BMI and manual control in M1, DLPFC, and Cd. We find that neural activity from DLPFC and M1 best distinguishes control types at the go cue and target acquisition, respectively, while M1 best predicts target-direction at both task events. We also find effective connectivity from DLPFC → M1 throughout both control types and Cd → M1 during BMI control. These results suggest distributed network activity between M1, DLPFC, and Cd during BMI control that is similar yet distinct from manual control.

    

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5. Transformation of speech sequences in human sensorimotor circuits

   https://doi.org/10.1073/pnas.1910939117  

   Müsch, Kathrin ; Himberger, Kevin ; Tan, Kean Ming ; Valiante, Taufik A. ; Honey, Christopher J. ( February 2020 , Proceedings of the National Academy of Sciences)

   After we listen to a series of words, we can silently replay them in our mind. Does this mental replay involve a reactivation of our original perceptual dynamics? We recorded electrocorticographic (ECoG) activity across the lateral cerebral cortex as people heard and then mentally rehearsed spoken sentences. For each region, we tested whether silent rehearsal of sentences involved reactivation of sentence-specific representations established during perception or transformation to a distinct representation. In sensorimotor and premotor cortex, we observed reliable and temporally precise responses to speech; these patterns transformed to distinct sentence-specific representations during mental rehearsal. In contrast, we observed less reliable and less temporally precise responses in prefrontal and temporoparietal cortex; these higher-order representations, which were sensitive to sentence semantics, were shared across perception and rehearsal of the same sentence. The mental rehearsal of natural speech involves the transformation of stimulus-locked speech representations in sensorimotor and premotor cortex, combined with diffuse reactivation of higher-order semantic representations. 

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