Probabilistic map of critical functional regions of the human cerebral cortex: Broca’s area revisited

Abstract

The organization of basic functions of the human brain, particularly in the right hemisphere, remains poorly understood. Recent advances in functional neuroimaging have improved our understanding of cortical organization but do not allow for direct interrogation or determination of essential (versus participatory) cortical regions. Direct cortical stimulation represents a unique opportunity to provide novel insights into the functional distribution of critical epicentres. Direct cortical stimulation (bipolar, 60 Hz, 1-ms pulse) was performed in 165 consecutive patients undergoing awake mapping for resection of low-grade gliomas. Tasks included motor, sensory, counting, and picture naming. Stimulation sites eliciting positive (sensory/motor) or negative (speech arrest, dysarthria, anomia, phonological and semantic paraphasias) findings were recorded and mapped onto a standard Montreal Neurological Institute brain atlas. Montreal Neurological Institute-space functional data were subjected to cluster analysis algorithms (K-means, partition around medioids, hierarchical Ward) to elucidate crucial network epicentres. Sensorimotor function was observed in the pre/post-central gyri as expected. Articulation epicentres were also found within the pre/post-central gyri. However, speech arrest localized to ventral premotor cortex, not the classical Broca's area. Anomia/paraphasia data demonstrated foci not only within classical Wernicke's area but also within the middle and inferior frontal gyri. We report the first bilateral probabilistic map for crucial cortical epicentres of human brain functions in the right and left hemispheres, including sensory, motor, and language (speech, articulation, phonology and semantics). These data challenge classical theories of brain organization (e.g. Broca's area as speech output region) and provide a distributed framework for future studies of neural networks.

Taking the brakes off the learning curve

“…The middle frontal areas that appear more activated after right cTBSCB in our study are the same areas that have been described to be associated with verbal fluency and sentence processing (Homae et al 2003;Tate et al 2014;McAvoy et al 2015) as well as constructive episodic memory (Addis et al 2009). Indeed, during the post-scan debriefing, the subjects reported almost always utilizing a kind of internal-speech for guiding and remembering the sequence, especially when starting to practice (singing, counting, internal-speaking etc.).…”

A probabilistic map of the human ventral sensorimotor cortex using electrical stimulation

“…Finally, the spatial scale is coarse and there is no access to the sulci, where a significant portion of cortical representations also reside. Modern imaging studies do not have the power to establish causality in the same way that stimulation does, 22 and therefore our findings can be an important reference for complementary noninvasive imaging studies. By monitoring for afterdischarges, we have ensured that the responses observed are not due to distant cortical spread of current.…”

“…1,9,21 Similarly, the probability map for speech arrest in the pars opercularis and precentral gyrus fits well with prior results. 18,22 There are a number of limitations to the present study that should be mentioned. First, stimulation data are limited by craniotomy exposure.…”

Neuroanatomical foundations of naming impairments across different neurologic conditions

“…Vascular lesions to posterior portions of the temporal cortex (figure 2, area 5), angular gyrus (figure 2, area 6), and inferior frontal gyrus, which includes Broca area (figure 2, area 7), have all been associated with anomia. 8,[21][22][23] Furthermore, likely due to several pathways connecting cortical areas to the diencephalon, stroke lesions affecting the thalamus can also lead to anomia. 24 Involvement of these cortical areas by other mechanisms can also result in anomia.…”