Phonological processing during language production: fMRI evidence for a shared production-comprehension network

Abstract

Studies of phonological processes during language comprehension consistently report activation of the superior portion of Broca's area. In the domain of language production, however, there is no unequivocal evidence for the contribution of Broca's area to phonological processing. The present event-related fMRI study investigated the existence of a common neural network for phonological decisions in comprehension and production by using production tasks most comparable to those previously used in comprehension. Subjects performed two decision tasks on the initial phoneme of German picture names (/ b / or not? Vowel or not?). A semantic decision task served as a baseline for both phonological tasks. The contrasts between each phonological task and the semantic task were calculated, and a conjunction analysis was performed. There was significant activation in the superior portion of Broca's area (Brodmann's area (BA) 44) in the conjunction analysis, also present in each single contrast. In addition, further left frontal (BA 45 / 46) and temporal (posterior superior temporal gyrus) areas known to support phonological processing in both production and comprehension were activated. The results suggest the existence of a shared fronto-temporal neural network engaged in the processing of phonological information in both perception and production. 

The role of the left Brodmann's areas 44 and 45 in reading words and pseudowords

“…(4) BA 44 receives its functionality by its integration in different anatomical circuits, as proposed, e.g., by Marshall and Fink [45]. This alternative is supported by the fact that the network for phonological decisions in language production and comprehension comprises at least BA 44 and the posterior superior temporal gyrus (pSTG) [10,33,34,69], whereas in the present study, the left ITG but not the pSTG was part of the network. (5) One of the first to third alternatives could apply in combination with the fourth.…”

“…In fact, data supporting this notion had been reported even earlier, e.g., by Démonet et al [18] and Zatorre et al [74,75] for auditory language comprehension. Later, these findings were extended to phonological processing in language production [33,34] and phonological working memory [77]. All these processes have in common the processing of phonological information.…”

Top–down and bottom–up processes in speech comprehension

“…In particular, the left inferior frontal gyrus (IFG), including Broca's area (Brodmann area [BA] 44 and BA45), seems to be involved in the processing of complex auditory stimuli. The data support a role for the left IFG in syntactic and phonological processing (Heim et al, 2003;Friederici et al, 2000). In addition, the area is associated with cognitive functions other than linguistic processing, such as working memory (Crinion et al, 2003;Mü ller et al, 2001;Specht et al, 2000).…”

“…Table 4 Mean and standard deviation of the onset of the standardized fMRI activation function with increasing signal-to-noise ratio (SNR) (left columns), and the asymptotic standardized fMRI amplitude obtained to stimuli presented above the high-intelligibility threshold (>À3.1 dB) (right columns) Region (BA) Side Onset of activation (dB SNR) Asymptotic amplitude (Z score) The first important finding of the current study is that only BA44 responded significantly to unintelligible speech at very low SNRs (SNRs less than À20.95 dB, LOWÀ category). It is well known that Broca's area is associated with both the production and perception of speech (Heim et al, 2003). In recent fMRI studies, decreasing SNRs of syllables and sentences presented in noise evoked increased activity in BA44 (Binder et al, 2004;Davis and Johnsrude, 2003).…”

“…Specifically, the pars opercularis of the left IFG has been associated with the building of the syntactic structure of sentences (Newman et al, 2003). Moreover, BA44 is involved in phonological working memory, i.e., the activation and maintenance of phonological representations during both language production (Heim et al, 2003) and perception (Wagner et al, 2000). The involvement of BA44 in these processes is consistent with the observed activity in BA44 in response to intelligible speech, and it is plausible that these processes are already initiated prior to the identification of speech.…”