Extended Data Fig. 8: Encoding Analysis of LFP Bands.

a. Semantic category prediction performance by LFP power band. Each column recreates the analysis of Fig. 4f and Fig. 4g, quantifying the percentage of channels significantly encoding a specific semantic category vs. other categories. Colours indicate distributions for 4 patients. LFP prediction was overall less significant than single units, with higher variability across patients. Beta and low gamma bands were the strongest predictors of semantic category. Overall, semantic category representation was significant but weaker than that of single units. Category discrimination was greatest in the beta band, followed by alpha, theta, and then low gamma. In the delta band, 50% of channels predicted one category and 2% of channels discriminated between 2 categories. In the theta band, 67% discriminated between 2 categories and 31% discriminated between 3 categories. In the alpha band, 60% of channels predicted 1 category, 26% discriminated between 3, and 19% discriminated between 4 categories. In the beta band, 80% of channels predicted 1 category, 50% discriminated between 3 categories, and 21% discriminated between 4. In the low gamma band, 71% of channels predicted 1 category and 20% of channels discriminated between 3 categories. In the gamma band, 50% of channels predicted 1 category and 25% of channels discriminated between 2. For both types of word feature, category discrimination using LFP was more variable across patients and categories than was observed in the single unit analysis. For example, proper nouns were discriminated in 100% of channels in the alpha band for one patient but 0% of channels in another. This observation may reflect the lower-dimensional signal content of LFP recordings, as well as their high signal correlation across densely packed channels of the Neuropixel array. b. Part of speech prediction performance by LFP power band. Each column recreates the analysis of Fig. 4i and Fig. 4j, quantifying the percentage of channels significantly encoding a specific part of speech vs. other categories. Colours indicate distributions for 4 patients. Part of speech discrimination by LFP power was overall less pronounced than semantic category discrimination but demonstrated comparable trends across bands. Part of speech discrimination was greatest in the beta band, followed by theta, then low gamma, and alpha. In the delta band, 39% of channels predicted one category and 1% of channels discriminated between 2 categories. In the theta band, 42% discriminated between 2 categories and 20% discriminated between 3 categories. In the alpha band, 50% of channels predicted 1 category, and 22% discriminated between 2. In the beta band, 42% of channels discriminated between 2 categories, 23% discriminated between 3 categories, and 8% discriminated between 4. In the low gamma band, 46% of cells predicted 1 category, 24% of cells discriminated between 2 categories, and 6% discriminated between 3. In the gamma band, 32% of cells predicted 1 category and 12% of cells discriminated between 2.