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5.0 Discussion

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Outline 5.0 Discussion

5.0 Discussion

5.1 Resting-State Support for a Supramodal Prefrontal Architecture

Our central hypothesis is supported by our RSFC results (Sections 4.1–4.3), where FEF couples preferentially with auditory-spatial and motion-sensitive areas - the ‘where’-stream. Meanwhile, IFJa couples selectively with the ‘what’-stream, with temporal-semantic and language-related areas. Applying single-seed and comparative partial correlation analyses, we observe a dissociation analogous to the spatial vs. non-spatial segregation previously established by Bedini & Baldauf (2021), suggesting FEF and IFJa as prefrontal control hubs not only for the visual but also for the auditory domain.

5.1.1 The FEF as an Auditory-Spatial Controller

The partial correlation results are consistent with the established role as a spatial attention controller and extend into the auditory domain. Rather than projecting to SPL regions typically associated with visual attention (7PC, 7Am, 7AL), the FEF couples selectively with the IPL, specifically PF and PFcm, and with the motion-sensitive area MST. Through this coupling, the FEF forms a clear auditory-spatial pathway with the IPL and MST, while the SPL connections vanish in partial correlation - unlike in visual analyses with FEF Bedini & Baldauf (2021). The FEF coupling with STV and TPOJ1 suggests that these regions function as multimodal convergence hubs (Rolls (2022) - NeuroImage). Alongside this ‘where’-coupling, the FEF also exhibits decoupling from all ventral temporal areas (e.g. TE1a, TA2, TGd).

This pattern aligns with the functional logic described by Rauschecker & Scott (2009) - Nature Neuroscience, who reviewed evidence that the posterodorsal auditory stream links posterior superior temporal cortex and parietal areas for spatial processing, with activation in regions adjacent to MT/MST specifically for auditory motion. Task-based fMRI supports this: Salmi (2009) demonstrated that top-down controlled shifts of auditory spatial attention recruit FEF/PMC alongside SPL and IPS, serving as evidence for FEF’s functional relevance in auditory spatial orienting. Our resting-state data extend this to the prefrontal level, suggesting that the FEF performs control over auditory spatial orienting, which operates within a multisensory framework (Rauschecker & Scott (2009) - Nature Neuroscience).

5.1.2 The IFJa as a Semantic-Auditory Controller

As shown in Section 4.3, the partial correlation pattern of the IFJa reveals a complementary picture to the FEF, coupling selectively with STS regions (STSdp, STSda), Broca’s areas BA44 and BA45, and early auditory association areas A4 and A5, but not exhibiting substantial coupling with parietal spatial areas. In direct contrast to FEF, this pattern is language- and object-identity-focused, and decouples from spatially parietal auditory regions.

This selectivity is consistent with the IFJa’s network and functional characterisation. Based on the resting-state parcellation of Ji et al. (2019, as reviewed in Bedini & Baldauf (2021)), the IFJa is assigned to the language network, placing it within the non-spatial semantic-language-domain. The results suggest that IFJa may perform top-down attention for auditory feature-extraction, object identity and semantic processing. The coupling with the Broca’s areas could also imply a role in the auditory object-related working memory system Bedini & Baldauf (2021). This is further consistent with the finding that top-down prefrontal control over auditory object processing is implemented via anticipatory alpha oscillations (De Vries & Baldauf (2021) - Journal of Neuroscience).

5.1.3 The How-Stream: FEF, 55b, and Auditory-Motor Integration

As shown in Section 4.2.2, the FEF’s strongest partial correlations are not with auditory regions at all, but with premotor-opercular regions 55b, SCEF, FOP1, and 43. This premotor pattern raises the question of whether the FEF performs auditory spatial control directly or is part of a broader network for auditory-motor integration. Hickok & Poeppel 2007 - Nature argued that the dorsal stream primarily serves auditory-motor integration for translating acoustic speech signals into articulatory motor plans. Our data are consistent with this view at the prefrontal level (Sections 4.2.1, 4.2.4): the FEF maintains spatial coupling with the IPL and MST, while its premotor connections via 55b and FOP1 suggest how-stream functions.

Seed-specificity analysis (Section 4.5) further supports this dissociation. When 55b is used as seed in comparison with FEF, it couples directly with early auditory association areas A4 and A5, connections absent from the FEF’s partial profile. This divergence suggests that 55b functions as the auditory-motor relay for early acoustic features (Dureux (2024)), while the FEF operates on a more abstract spatial coordinate system. Therefore, the FEF may serve as the pure spatial controller, supplying abstract coordinates to the 55b-anchored how-stream without engaging in low-level acoustic processing itself.
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5.1.4 A Supramodal Prefrontal Architecture

To summarise the global connectivity findings, there is converging evidence that FEF and IFJa function as prefrontal attention hubs not only for vision, but also for audition. One could interpret this as a multimodal organisation (Ghazanfar & Schroeder (2006)), implying that these hubs simply perform attention for both modalities through independent, parallel pathways, processing visual and auditory stimuli separately but within the same regions. We argue for a stronger interpretation: FEF and IFJa are supramodal. Spagna et al. (2015) proposed that executive control of attention operates supramodally, coordinating behaviour across modalities through shared neural mechanisms, instead of alerting and orienting processes, which remain modality-specific. Our RSFC results are consistent with this view at the anatomical level: FEF and IFJa do not merely respond to both vision and audition, but implement the same organisational principle: spatial versus non-spatial top-down control, independent of the sensory modality (Bedini & Baldauf (2021)).
The results suggest a domain-general architecture at the level of attentional control. This is consistent with the evolutionary argument that visuospatial attention systems are preserved in primates and later also recruited other sensory domains Bedini & Baldauf (2021). Whether these RSFC coupling patterns reflect true genuine top-down control signals still needs to be explored with directed connectivity methods (De Vries & Baldauf (2021) - Journal of Neuroscience). The present findings represent a first step towards this hypothesis, further implications are discussed in Section 5.6.

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5.2 Re-evaluating the auditory where stream

In the visual domain, FEF is strongly coupled with 7PC/7Am; in the auditory domain, however, FEF recruits inferior parietal regions (PF, PFop, PFcm) in the partial correlation, while still correlating with motion-sensitive area MST, possibly reflecting FEF’s role in supramodal motion integration. This dissociation aligns with the literature and with known differences in auditory and visual spatial network topology. The direct coupling with multisensory convergence hub TPOJ1 further supports this argumentation. Together, these patterns suggest that FEF functions as a shared supramodal controller that recruits modality-appropriate parietal regions. Rauschecker & Scott (2009) - Nature Neuroscience show that the auditory dorsal stream is spatial; the present analysis extends this view to the prefrontal level, proposing FEF as the attentional hub for audition.
Taken together, the selective coupling of FEF with inferior parietal and motion-sensitive regions positions it as the prefrontal controller of the auditory ‘where’-stream, operating through modality-appropriate cortical pathways.

The FEF’s strongest direct connections in the auditory domain are premotor and frontal opercular (SCEF, 55b, area 43, FOP1, and FOP3) rather than the superior parietal regions associated with visual spatial attention. This is consistent with the view proposed by Hickok and Poeppel (2004), in which the dorsal auditory stream serves sound-to-action mapping rather than spatial localisation alone. This creates an honest tension: is FEF primarily a ‘where’ hub or a ‘how’ hub? The dominance of motor connections suggests that the dorsal stream may be better understood as a spatial-motor integration pathway, with FEF coordinating both spatial orienting and motor-action preparation, a view in which ‘where’ and ‘how’ are not mutually exclusive but complementary aspects of top-down auditory control.

5.2.3 55b as an Auditory-Motor Relay

Comparing 55b to FEF, 55b shows strong coupling with both FEF and IFJa, as well as regions of the ‘what’-stream. Notably, 55b maintains direct functional access to A4 and A5, whereas FEF does not, suggesting a functional division of labour: FEF encodes higher-order spatial information, while 55b serves as its acoustic relay into the auditory hierarchy. 55b may thus receive spatial commands from FEF and translate them into the semantic-auditory system. This is further supported by 55b’s stronger coupling with motor areas relative to FEF. Together, these findings suggest the dorsal stream is not monolithic but reflects a dissociation between FEF as a supramodal spatial-motor controller and 55b as an auditory-language integration hub.

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5.3 Re-evaluating the auditory 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.

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5.4 Anatomical Ambiguities

Assigning ROIs to the correct streams was anything but straightforward, given divergent accounts in the literature - most notably between Rolls et al. (2023) and Glasser et al. (2016). The former use effective connectivity to trace directional information flow, capturing output projections regardless of a region’s primary functional identity. The latter, on the other hand, rely on myeloarchitecture, cortical thickness, RSFC and task-fMRI activation profiles to classify areas by their dominant functional role. These methods answer different questions. Effective connectivity reveals that A4 and A5 maintain output channels to dorsal motion areas, while Glasser’s parcellation shows their dominant activation is language-related. Our resting-state partial correlation serves as a methodological middle ground: by partialling out the competing seed region, it isolates which prefrontal hub preferentially governs each region, and this is the criterion on which we resolved stream assignments.

Areas A4 and A5. Both showed robust coupling with IFJa; only A4 showed slight connectivity with FEF. Glasser’s argument where A4 and A5 are both activated in LANGUAGE STORY contrast - which is connected to IFG (44, 45, 47l) - supports the membership to the ‘what’-stream. Since A5 is also inferior to A4, this leads A5 more to the ventral pathway, which reflects the connectivity pattern. Whereas A4 might rather function as a router for information flow to higher level areas in mainly the ‘what’-stream. Rolls’ argument of A4/A5 demonstrating EC with MT and MST does not conflict with our results, since this reflects an indirect route to FEF. This might reflect a divergence hub, distributing information to both ‘what’ and ‘where’-pathways.

PSL. The PSL shows an interesting pattern, where it couples with IFJa left-hemispherically and with FEF right-hemispherically (Section 4.4.2). Additionally, Dureux (2024) argues that PSL is not responsive to auditory stimuli at all, which might reflect PSL as an abstract, modality-independent level, not on acoustic features. This is further supported by Rolls et al. (2023), who show directional EC from STS regions into PSL. PSL might serve as a supramodal connector or a high-level convergence hub, left side to semantic identity via IFJa, while right side links to spatial attention via FEF. It is interesting that a region which does not respond to any acoustic stimuli couples strongly with both prefrontal attention hubs, which could imply that top-down connections do not require bottom-up auditory drive at PSL.

STV. In the partial correlation analysis, STV couples with both prefrontal seeds at comparable strength (Section 4.4.3), making a clear stream assignment on connectivity strength alone impossible. Rolls et al. (2023), however, classify STV within the ventral language network, and Glasser et al. (2016) further report activation in social cognition and theory-of-mind task contrasts — both consistent with a primary what-stream affiliation. Together, these findings position STV as a multimodal interface within the ‘what’-stream, accessed by both top-down attention hubs.

Broca’s Areas 44 and 45. We used the Broca seed validation (Section 4.5.2) to analyse the connectivity patterns of both regions, since Rolls et al. (2023) argue for a dissociation where 45 belongs to an auditory ventral pathway, while 44 might form a dorsal stream. The results reveal a clear functional dissociation: Area 45 anchors the semantic ‘what’-stream via strong temporal coupling, while Area 44 orients toward motor-articulatory circuits via 55b and AVI. The cross-hemispheric 55b coupling of both areas suggests partial overlap rather than a strict boundary. Importantly, Area 44 shows no meaningful mean connectivity to FEF, despite a significant z-score, placing it within the ‘what’-stream rather than a dorsal spatial-motor framework.

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5.5 Predictive Modelling

1. Subheading

Hier schreiben…

2. Subheading

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5.6 Limitations & Future Directions

5.6.1 Limitations

Most imp, resting-state fMRI analysis has the advantage

Indirect Nature of Resting-State fMRI

Absence of an Auditory Spatial Task in the HCP Battery

Glasser Atlas Granularity

ROI Exclusion

5.6.2 Future Directions

1. Effective Connectivity

2. MEG for Oscillatory Signatures

3. Dedicated Auditory Spatial Task

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