Network dynamics of Broca's area during word selection.

Current models of word-production in Broca's area (i.e. left ventro-lateral prefrontal cortex, VLPFC) posit that sequential and staggered semantic, lexical, phonological and articulatory processes precede articulation. Using millisecond-resolution intra-cranial recordings, we evaluated spatiotemporal dynamics and high frequency functional interconnectivity between left VLPFC regions during single-word production. Through the systematic variation of retrieval, selection, and phonological loads, we identified specific activation profiles and functional coupling patterns between these regions that fit within current psycholinguistic theories of word production. However, network interactions underpinning these processes activate in parallel (not sequentially), while the processes themselves are indexed by specific changes in network state. We found evidence that suggests that pars orbitalis is coupled with pars triangularis during lexical retrieval, while lexical selection is terminated via coupled activity with M1 at articulation onset. Taken together, this work reveals that speech production relies on very specific inter-regional couplings in rapid sequence in the language dominant hemisphere

Category Selectivity for Face and Scene Recognition in Human Medial Parietal Cortex

The rapid recognition and memory of faces and scenes implies the engagement of category-specific computational hubs in the ventral visual stream with the distributed cortical memory network. To better understand how recognition and identification occur in humans, we performed direct intracranial recordings, in a large cohort of patients (n = 50), from the medial parietal cortex (MPC) and the medial temporal lobe (MTL), structures known to be engaged during face and scene identification. We discovered that the MPC is topologically tuned to face and scene recognition, with clusters in MPC performing scene recognition bilaterally and face recognition in right subparietal sulcus. The MTL displayed a selectivity gradient with anterior, entorhinal cortex showing face selectivity and posterior parahippocampal regions showing scene selectivity. In both MPC and MTL, stimulus-specific identifiable exemplars led to greater activity in these cortical patches. These two regions work in concert for recognition of faces and scenes. Feature selectivity and identity-sensitive activity in the two regions was coincident, and they exhibited theta-phase locking during face and scene recognition. These findings together provide clear evidence for a specific role of subregions in the MPC for the recognition of unique entities.12 month embargo; published online: 4 June 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Temporal Dynamics of Human Frontal and Cingulate Neural Activity During Conflict and Cognitive Control

Cognitive control refers to the ability to produce flexible, goal-oriented behavior in the face of changing task demands and conflicting response tendencies. A classic cognitive control experiment is the Stroop-color naming task, which requires participants to name the color in which a word is written while inhibiting the tendency to read the word. By comparing stimuli with conflicting word-color associations to congruent ones, control processes over response tendencies can be isolated. We assessed the spatial specificity and temporal dynamics in the theta and gamma bands for regions engaged in detecting and resolving conflict in a cohort of 13 patients using a combination of high-resolution surface and depth recordings. We show that cognitive control manifests as a sustained increase in gamma band power, which correlates with response time. Conflict elicits a sustained gamma power increase but a transient theta power increase, specifically localized to the left cingulate sulcus and bilateral dorsolateral prefrontal cortex (DLPFC). Additionally, activity in DLPFC is affected by trial-by-trial modulation of cognitive control (the Gratton effect). Altogether, the sustained local neural activity in dorsolateral and medial regions is what determines the timing of the correct response