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An index to probe cortical excitability
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DOI：10.1088/1741-2552/ae5559.png)
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Abstract
En 中文
Objective. Cortical excitability can be defined as the cortex’s responsiveness to incoming stimuli. It can be probed with brain stimulation, either globally and non-invasively, using transcranial magnetic stimulation or locally through direct electrical stimulation of the cortex. Here, we establish a method to quantify cortical excitability over its dynamical range, applying stimulation of increasing intensities and recording growing cortical responses via intracranial (i)EEG from patients with pharmacoresistant epilepsy to construct so-called stimulation-response curves (SRC). Approach. We propose a practical framework for (i) identifying effective cortical connections of different strength using Spearman’s rank correlation on the SRC, (ii) characterizing their linear or non-linear dynamics using two- to five-parameter fits of the measured SRC and (iii) extracting the excitability index (ExI), a unitless quantity between 0 and 1 - the area under the normalized SRC - that estimates the excitability of a given cortico-cortical connection. The robustness of this framework was characterized in a series of sensitivity and power analyses, in which a data set of 9024 single-trial stimulations among 12 participants was subsampled. Results. Across brain regions, we found a total of 974 (34.5%) effective connections ( 0.005 FDR-corrected, Spearman correlation). A majority showed a non-linear stimulation-response relationship (R2 = 0.89 ± 0.12), and a five-parameter sigmoid fit was necessary in 30% of cases, justifying the added complexity (Akaike information criterion). To illustrate the clinical relevance of the proposed approach, we analyze the change in excitability in 4 patients pre- and post-medication (0.5–1 mg clonazepam, intravenously). Significance. We present a framework to probe, measure, fit, and quantify the excitability of cortico-cortical connections in practice. Our proposed ExI provides a simple way to measure and compare cortical excitability across recorded brain areas, participants and conditions.
Keywords:
cortical excitability
stimulation-response curves
intracranial EEG
excitability index
cortico-cortical connections
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