Timing and location of speech errors induced by direct cortical stimulation

Area of Science:

• Neuroscience
• Neurosurgery
• Speech Production

Background:

• Direct electrocortical stimulation is the gold standard for mapping eloquent cortical regions during neurosurgery.
• However, this method lacks specificity regarding the underlying cognitive processes affected.
• Understanding temporal dynamics of speech arrest can differentiate region-specific functions.

Purpose of the Study:

• To map the temporal dynamics of speech arrest across peri-sylvian cortices.
• To quantify the latency between stimulation and speech deficits to differentiate cognitive processes.
• To substantiate hypotheses about distinct region-specific functional roles in speech production.

Main Methods:

• Retrospective observational study of 20 epilepsy patients undergoing intracranial EEG monitoring.
• Automatic speech task during clinical bedside language mapping.
• Latency to speech arrest calculated from stimulation onset to speech arrest onset, controlling for individual speech rate.

Main Results:

• Motor-based speech arrest predominantly occurred in sensorimotor cortex with mid-range latencies (peak at 0.47s).
• Shorter latencies were observed in supramarginal gyrus (0.46s), superior temporal gyrus (0.51s), and middle temporal gyrus (0.54s), suggesting motor execution interference.
• Longer latencies in inferior frontal gyrus (0.95s) and ventral sensorimotor cortex indicated interference with higher-level speech planning.

Conclusions:

• Speech arrest latency predicts the underlying cognitive process disrupted by cortical stimulation.
• Temporoparietal regions (supramarginal and superior temporal gyri) are involved in motor execution of speech.
• Inferior frontal gyrus and ventral sensorimotor cortex are implicated in the planning stages of speech production.