Outline 5.3 Re-evaluating the auditory what stream
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5.3 Re-evaluating the auditory what stream
5.3.1 The Semantic Link (‘What’-Stream)
The IFJa’s partial correlation profile is the mirror image of FEF’s in the ‘what’-stream. It couples with STS regions (STSdp, STSda) and with early auditory areas A4/A5, but not with dorsal spatial parietal regions. The systematic absence of parietal coupling in the partial correlation single-seed analysis of IFJa confirms the dissociation of auditory attention. In comparison to Bedini & Baldauf (2021), where IFJa encodes object-based attention in the visual domain, the present RSFC results suggest that IFJa may implement the same principle for auditory identity and semantic attention, positioning it as the primary prefrontal source of top-down modulation in the auditory domain and further supporting the supramodal hypothesis of prefrontal attention.
5.3.2 IFJa as Executive Hub of the Language Network
The coupling of IFJa shows a bilateral connectivity with all IFG subregions (44, 45, 47l). The comparative partial correlation profiles of Areas 44 and 45 (Section 4.5.4) further specify IFJa’s coordinating role: Area 45 couples preferentially with temporal-semantic regions (STS, PSL) and exhibits stronger left-hemisphere dominance, consistent with the classical left lateralisation of semantic language processing (Hickok & Poeppel, 2007). Area 44, by contrast, concentrates its coupling in articulatory-premotor circuits (AVI, 55b). Crucially, IFJa maintains bilateral connectivity to both areas, positioning it as a bilateral prefrontal hub that projects onto a predominantly left-lateralized language system.
If IFJa functions as the attention hub for the auditory-semantic pathway, this implies strong inter-prefrontal connectivity between dorsal and ventral auditory streams. IFJa might engage with 45 for semantic processing and with 44 for articulatory-motor response preparation. This is consistent with Rolls et al. (2023), where area 45 is involved in semantic processing and 44 could be part of a dorsal language stream. Though, a caveat points out that in the right hemisphere area 45 is more strongly correlated with premotor areas than area 44, which might suggest that semantic processing extends into the premotor domain of the dorsal stream.
5.3.3 A5 as the Auditory Entry Point into the What-Stream
Both A4 and A5 show coupling to IFJa, with A5 exhibiting stronger correlations in the left hemisphere. A5 may therefore function as the primary gateway from early auditory cortex into the ‘what’-stream (for a full treatment of A5’s anatomical ambiguity and stream assignment, see Section 5.4). With A5 integrated into this network, IFJa operates across the entire ‘what’-stream hierarchy from the IFG to early auditory cortex, providing first evidence for IFJa as a central prefrontal attention hub for the full auditory ‘what’-stream. It is possible that IFJa modulates early auditory features at the level of A5, which are then converted into semantic representations and object identity at more anterior stages.