Nouns and verbs in the intact brain: Evidence from event-related potentials and high-frequency cortical responses

Lesion evidence indicates that words from different lexical categories, suc h as nouns and verbs, may have different cortical counterparts. In this stu dy, processing of nouns and verbs was investigated in the intact brain usin g (i) behavioral measures, (ii) stimulus triggered event-related potentials and (iii) high-frequency electrocortical responses in the gamma band. Noun s and verbs carefully matched for various variables, including word frequen cy, length, arousal and valence, were presented in a lexical decision task while electrocortical responses were recorded. In addition, information abo ut cognitive processing of these stimuli was obtained using questionnaires and reaction times. As soon as similar to 200 ms after stimulus onset, even t-related potentials disclosed electrocortical differences between nouns an d verbs over widespread cortical areas. In a later time window, 500-800 ms after stimulus onset, there was a significant difference between high-frequ ency responses in the 30 Hz range. Difference maps obtained from both event -related potentials and high-frequency responses revealed strong between-ca tegory differences of signals recorded above motor and visual cortices. Beh avioral data suggest that these different physiological responses are relat ed to semantic associations (motor or visual) elicited by these word groups . Our results are consistent with a neurobiological model of language repre sentation postulating cell assemblies with distinct cortical topographies a s biological counterparts of wards. Assemblies representing nouns referring to visually perceived objects may include neurons in visual cortices, and assemblies representing action verbs may include additional neurons in moto r, premotor and prefrontal cortices. Event-related potentials and high-freq uency responses are proposed to indicate two different functional states of cell assemblies: initial full activation ('ignition') and continuous rever beratory activity.