Cortical activation patterns of affective speech processing depend on concurrent demands on the subvocal rehearsal system - A DC-potential study

In order to delineate brain regions specifically involved in the processing of affective components of spoken language (affective or emotive prosody), we conducted two event-related potential experiments. Cortical activation patterns were assessed by recordings of direct current components of the EE G signal from the scalp. Right-handed subjects discriminated pairs of decla rative sentences with either happy, sad or neutral intonation. Each stimulu s pair was derived from two identical original utterances that, due to digi tal signal manipulations, slightly differed in fundamental frequency (F0) r ange or in duration of stressed syllables. In the first experiment, subject s were asked: (i) to denote the original emotional category of each sentenc e pair and (ii) to decide which of the two items displayed stronger emotion al expressiveness. Participants in the second experiment were asked to repe at the utterances using inner speech during stimulus presentation in additi on to the discrimination task. In the absence of inner speech, a predominan t activation of right frontal regions was observed, irrespective of emotion al category. In the second experiment, a bilateral activation with left fro ntal preponderance emerged from discrimination during additional performanc e of inner speech. Compared with the first experiment, a new pattern of aco ustic signal processing arose. A relative decrease of brain activity during processing of F0 stimulus variants was observed together with increased ac tivation during discrimination of duration-manipulated sentence pairs. Anal ysis of behavioural data revealed no significant differences in evaluation of expressiveness between the two experiments. We conclude that the topogra phical shift of cortical activity originates from left hemisphere (LH) mech anisms of speech processing that centre around the subvocal rehearsal syste m as an articulatory control component of the phonological loop. A strong c oupling of acoustic input and (planned) verbal output channel in the LH is initiated by subvocal articulatory activity like inner speech. These neural networks may provide interpretations of verbal acoustic signals in terms o f motor programs and facilitate continuous control of speech output by comp aring the signal produced with that intended. Most likely, information on m otor aspects of suprasegmental signal characteristics contributes to the ev aluation of affective components of spoken language. In consequence, the ri ght hemisphere (RH) holds a merely relative dominance, both for processing of F0 and for evaluation of emotional significance of sensory input. Psycho physically, an important determinant on expression of lateralization patter ns seems to be given by the degree of communicative demands such as solely perceptive (RH) or perceptive and verbal-expressive (RH and LH).