Electrophysiological evidence of functional integration between the language and motor systems in the brain: a study of the speech Bereitschaftspotential

Abstract

Objective: We investigated whether the Bereitschaftspotential (BP), an event related potential believed to reflect motor planning, would be modulated by language-related parameters prior to speech. We anticipated that articulatory complexity would produce effects on the BP distribution similar to those demonstrated for complex limb movements. We also hypothesized that lexical semantic operations would independently impact the BP.

Methods: Eighteen participants performed 3 speech tasks designed to differentiate lexical semantic and articulatory contributions to the BP. EEG epochs were time-locked to the earliest source of speech movement per trial. Lip movements were assessed using EMG recordings. Doppler imaging was used to determine the onset of tongue movement during speech, providing a means of identification and elimination of potential artifact.

Results: Compared to simple repetition, complex articulations produced an anterior shift in the maximum midline BP. Tasks requiring lexical search and selection augmented these effects and independently elicited a left lateralized asymmetry in the frontal distribution.

Conclusions: The findings indicate that the BP is significantly modulated by linguistic processing, suggesting that the premotor system might play a role in lexical access.

Significance: These novel findings support the notion that the motor systems may play a significant role in the formulation of language.

Fig. 1

Synchronous recordings of articulation related movement from the tongue, lip, and phonogram during single word utterance. (A) For the word “Piranha” lip movement begins 220 ms prior to the onset of tongue movement and 600 ms prior to the phonation. (B) For the word “Dog” tongue movement begins 335 ms prior to the onset of lip movement and 417 ms prior to the phonation.

Fig. 2

Bereitschaftspotential waveforms from right hand finger flexions (top left) and simple speech (top right). Topographic maps of the mean amplitude from −2000 to 0 ms prespeech are shown on the bottom.

Fig. 3

Mean articulator movement onset latencies from visual cues. No significant latency differences were found between conditions.

Fig. 4

Comparison of averaged BP waveforms from anterior (FCz) and posterior (Cz) midline electrodes, in the verbal fluency (VF), word reading (WR), and simple speech (SS) conditions.

Fig. 5

Comparison of averaged BP waveforms from left (F3) and right (F4) frontal electrodes, in the verbal fluency, word reading, and simple speech conditions.

Fig. 6

Topographic voltage maps of BP amplitude from −2000 ms to speech onset from the verbal fluency, word reading, and simple speech conditions.