4.1 Global Connectivity Patterns

Outline 4.1 Global Connectivity Patterns

• Global erklären
• SLF nutzen?
• 44 vs 45 nochmal drüberlesen

To-Do’s

• 44 eher auf FEF seite packen
• FEF Teil ist viel zu groß und IFJ part viel zu kurz
• neue Plots generieren mit besseren Visuals
• den Teil mit HCP language task rausnehmen

4.1 Global Connectivity Patterns

Before examining each stream individually, we assess the overall functional dissociation between the auditory ‘what’ and ‘where’ streams. Using full and partial correlation, we compare the connectivity profiles of the two prefrontal seed regions FEF and IFJa, and validate their anatomical specificity against neighbouring control seeds.

4.1.1 FEF vs. IFJa: Validation of Prefrontal Seed Regions

To validate the anatomical specificity of our seed regions, we compared their partial correlation connectivity fingerprints across both hemispheres.

Figure 4.X: Circular connectivity diagrams comparing FEF (red) and IFJa (blue) full correlation with all auditory target ROIs, left (A) and right (B) hemisphere. The full correlation profiles reveal broad network-wide co-activation, including strong FEF coupling with superior parietal areas (7Am, 7PC, OP4) and IFJa coupling with temporal-semantic regions. These unpartialled patterns reflect general network membership and shared variance; partial correlation (Figure 4.X) isolates the direct functional pathways.

The functional connectivity analysis with full correlation reveals a clear double dissociation with FEF significantly coupling with spatial-parietal areas (full corr.: OP4 $z=21.13$, $\overline{r}=0.31$; 7Am $z=24.44$, $\overline{r}=0.38$; 7PC $z=23.53$, $\overline{r}=0.30$; RH) with exceptions of FEF coupling with TA2 (full corr.: $z=16.34$, $\overline{r}=0.21$; RH) stronger than IFJa and TA2 and 55b connecting stronger to IFJa than to FEF.

Then we applied partial correlation to partial out third party connectors to see a clear picture of the connectivity patterns within the auditory streams. The partial correlation analysis reveals that the most direct auditory connections to FEF are consistently rooted in the spatial orienting network. Both hemispheres show strong coupling with the inferior parietal cluster (PF, PFop, PFcm). However, the network shows a distinct right-hemispheric dominance in specific regions, consistent with widely accepted right-lateralisation framework for spatial auditory processing (Hickok & Poeppel, 2007). While the left hemisphere dominates in FOP3 ($z=3.43$, $\overline{r}=0.00$), 7Am ($z=8.37$, $\overline{r}=0.00$) and 7PC ($z=5.82$, $\overline{r}=0.00$), the right hemisphere demonstrates a clear dominance in PF (right $z=18.15$, $\overline{r}=0.03$; left $z=8.61$, $\overline{r}=0.02$) and shows partial correlation with the perisylvian language area (PSL, $z=12.64$, $\overline{r}=0.03$), suggesting a stronger specialised right-lateralized fronto-parietal integration for spatial auditory processing (Hickok & Poeppel 2007 - Nature).

Figure 4.1: Functional connectivity heatmap comparing FEF and IFJa partial correlation z-scores across 36 auditory target ROIs, left hemisphere. Warm colours (yellow-orange) indicate positive coupling; cool colours indicate near- zero or negative coupling. The opposing colour patterns between FEF and IFJa rows reveal the double dissociation: FEF couples preferentially with spatial-parietal and motor regions, while IFJa couples preferentially with temporal-semantic regions.

Figure 4.X: Circular connectivity diagrams comparing FEF (red) and IFJa (blue) partial correlation with all auditory target ROIs, left (A) and right (B) hemisphere. Each arc segment represents one ROI; line thickness and colour indicate the magnitude and direction of preferential coupling. Spatial-motor ROIs (inferior parietal, premotor) couple predominantly with FEF; temporal-semantic ROIs (STS, Broca areas) couple predominantly with IFJa.

Figure 4.X: FEF versus IFJa partial correlation connectivity projected onto the cortical surface, left (A) and right (B) hemisphere. Red regions indicate preferential FEF coupling; blue regions indicate preferential IFJa coupling. The contrast between parietal and motor cortex (FEF, red) versus superior temporal sulcus and Broca’s area (IFJa, blue) visualises the double dissociation across both hemispheres.

• FEF: The FEF seed exhibits robust full correlation with the superior parietal lobe (7AL, 7Am, 7PC). This replicates the where-stream, similar to the visual stream Bedini & Baldauf (2021), together with auditory and motor regions such as A5, PBelt, FOP1, STV and PSL
• IFJa: In contrast, the IFJa showed strong coupling with the anterior language network (HCP language task)

4.1.2 Topographical Validation: IFJp Control Seed

To validate the top-down control over the auditory what-stream is driven by the anterior subdivision of IFJ, a control partial correlation model substituted IFJa for IFJp, its immediate neighbour.
The control analysis confirms the functional dissociation of where and what stream. The FEF maintains its robust connectivity to the dorsal auditory and motor network with 23 significant regions in the left and 20 in the right hemisphere.

Figure 4.X: Specificity control: FEF (red) versus IFJp (grey) partial correlation circular diagrams, left (A) and right (B) hemisphere. Substituting IFJa with its immediate posterior neighbour IFJp substantially reduces temporal coupling, confirming that top-down control over the auditory ‘what’-stream is specific to the anterior IFJ subdivision and does not generalise to adjacent prefrontal regions.

In the profound contrast substituting the what-hub with IFJp leads to a significant drop in the connectivity pattern of the semantic what-stream. The IFJp fails to communicate with the temporal lobe in comparison to the FEF.
This contrast provides the evidence that the prefrontal control hub over auditory identity processing is functionally exclusively anchored in the IFJa.