Intracranial identification of an electric frontal-cortex response to auditory stimulus change: a case study

The aim of the present study was to clarify whether ERPs recorded directly from the human frontal cortex contributed to the auditory N1 and mismatch n egativity (MMN) elicited by changes in non-phonetic and phonetic sounds. We examined the role of prefrontal cortex in the processing of stimulus repet ition and change in a 6-year-old child undergoing presurgical evaluation fo r epilepsy. EEG was recorded from three bilateral sub-dural electrode strip s located over lateral prefrontal areas during unattended auditory stimulat ion. EEG epochs were averaged to obtain event-related potentials (ERPs) to repeating (standard) tones and to infrequent (deviant) shorter duration ton es and complex sounds (telephone buzz). In another condition, ERPs were rec orded to standard and deviant syllables, /ba/ and /da/, respectively. ERPs to vibration stimuli delivered to the fingertips were not observed at any o f the sub-dural electrodes, confirming modality specificity of the auditory responses. Focal auditory ERPs consisting of P100 and N150 deflections wer e recorded to both tones and phonemes over the right lateral prefrontal cor tex. These responses were insensitive to the serial position of the repeati ng sound in the stimulus train. Deviant tones evoked an MMN peaking at arou nd 128 ms. Deviant complex sounds evoked ERPs with a similar onset latency and morphology bur with an approximately two-fold increase in peak-to-peak amplitude. We conclude that right lateral prefrontal cortex (Brodmann's are a 45) is involved in early stages of processing repeating sounds and sound changes. (C) 2001 Elsevier Science B.V. All rights reserved.