Non-invasive methods to image activity in the human brain are improving steadily, but still suffer from considerable shortcomings in terms of spatial and temporal resolution. Under special clinical conditions, it is possible to measure directly the neuronal activity from regions of the human brain. Electro-physiological recordings can be made chronically from electrodes placed in the depth or on the surface of the brain to localize the origin and spread of seizure-related activity in patients with medically intractable epilepsy. Investigations that piggyback on this clinically driven invasive methodology are particularly valuable in the study of higher cognitive functions for which animal models can be difficult and sometimes impossible. Intracranial recordings from epileptic patients have thus contributed substantially to our knowledge about language functions in the human brain. In particular, they have highlighted the involvement of non-perisylvian brain regions in the system of distributed brain regions that orchestrates language usage.

Two brain areas within the more densely sampled terrain of the inferior occipital and temporal regions have been identified - along the posterior and anterior portions of the fusiform gyrus. Both regions show specialization for processing verbal material, and are nearby to areas that are dedicated to processing face stimuli. The posterior region is not influenced by the semantic content or context of the stimuli, but is strongly affected by selective attention. The anterior region, in the anterior medial temporal cortex underlying the hippocampus, is sensitive to both the content and the context of word stimuli, and is also modulated by selective attention. The nearby face-selective areas show a parallel progression of sensitivity to semantic factors, with only the anterior region being sensitive to the familiarity and context of the face. The intracranial findings therefore support the existence of nodes that are functionally specialized for treating verbal material within the ventral object-recognition system.

Complementary methodology for studying the human brain has confirmed the involvement of these brain areas within the language network, and has helped constrain the interpretations regarding their contributions. The posterior node may subtend visual analysis of word shapes, participating in orthographic computations. The anterior node may provide an interface between language and associative long-term memory functions, weaving the word representations, perhaps multimodally, with the ongoing context. The discovery of these additional nodes specialised for verbal material has greatly enriched the formulation of language implementation in the human brain.

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