Brain basis of auditory comprehension

Initial acoustic-phonological processes take place during the first 100 ms after acoustic stimulation crucially involve the primary auditory cortex (PAC) and the planum temporale (PT). From these regions, the information is transferred both to the anterior and the posterior superior temporal gyrus (STG) and sulcus (STS). The left anterior STS is sensitive to the intelligibility of a stimulus. The anterior STG, together with the left frontal operculum (FOP) connected via a ventral pathway (Ventral Pathway II, see Figure 13C) through the uncinate fasciculus (UF), builds the neural network for initial local structure building processes. During a second processing step semantic, grammatical and thematic relations in a sentence are processed in parallel systems, activating separable left-lateralized temporo-frontal networks. The semantic network involves the middle and posterior STG/MTG (sometimes extending into anterior temporal regions) and BA 45 (and BA 47) in the frontal cortex connected via another ventral pathway (Ventral Pathway I, see Fig. 13C) through the extreme capsule fiber system (ECFS). The syntactic network dealing with complex sentence structures involves BA 44 as part of Broca's area in the frontal cortex and the posterior STG/STS connected via a dorsal pathway (Dorsal pathway II, see 13C). Note, that Dorsal Pathway I connecting the temporal cortex to the premotor cortex is supposed to support sensory-to-motor mappings (see Fig. 13C). Syntactic and semantic integration processes take place during a third processing step, possibly under the involvement of the posterior STG/STS and the Basal Ganglia.

The processing of suprasegmental prosodic information is supported by the right hemisphere. The interaction of syntactic information processed in the left hemisphere and prosodic information processed in the right hemisphere is supported by the posterior portion of the corpus callosum, the structure which connects the temporal cortices of the two hemispheres.