Auditory cortical connectivity in humans

Abstract

To understand auditory cortical processing, the effective connectivity between 15 auditory cortical regions and 360 cortical regions was measured in 171 Human Connectome Project participants, and complemented with functional connectivity and diffusion tractography. 1. A hierarchy of auditory cortical processing was identified from Core regions (including A1) to Belt regions LBelt, MBelt, and 52; then to PBelt; and then to HCP A4. 2. A4 has connectivity to anterior temporal lobe TA2, and to HCP A5, which connects to dorsal-bank superior temporal sulcus (STS) regions STGa, STSda, and STSdp. These STS regions also receive visual inputs about moving faces and objects, which are combined with auditory information to help implement multimodal object identification, such as who is speaking, and what is being said. Consistent with this being a “what” ventral auditory stream, these STS regions then have effective connectivity to TPOJ1, STV, PSL, TGv, TGd, and PGi, which are language-related semantic regions connecting to Broca’s area, especially BA45. 3. A4 and A5 also have effective connectivity to MT and MST, which connect to superior parietal regions forming a dorsal auditory “where” stream involved in actions in space. Connections of PBelt, A4, and A5 with BA44 may form a language-related dorsal stream.

Anatomy of the auditory cortex then and now

“…The following conclusions can be drawn from the study by Rolls et al. (2023): Measurements of effective connectivity, complemented by functional connectivity and diffusion tractography, provide evidence consistent with a hierarchy of auditory cortical processing in humans inferred from anatomical tracer studies in nonhuman primates (Kaas & Hackett, 2000; Pandya, 1995): from a Core region (A1) to Belt regions LBelt and MBelt, then to PBelt, and finally on to higher regions (A4 and A5; see also Rauschecker & Scott, 2009). A4 has connectivity to TA2 in the anterior temporal lobe, which makes it part of a ventral auditory stream implicated in semantic object processing (Rauschecker & Scott, 2009; Rauschecker & Tian, 2000).…”

“…These STS regions also receive visual inputs about moving faces and objects, and the auditory and visual streams are combined to help in multimodal object identification, such as who is speaking, what is being said, what the object is, and so on. This system can thus also be considered as an important part of the ventral auditory “what” stream. Consistent with the dorsal‐bank STS regions being part of a ventral auditory stream, the dorsal‐bank STS regions then have effective connectivity to TPOJ1, STV, PSL, TGv, TGd, and PGi, which are language‐related regions involved in semantic representations about objects, faces, and so on using multimodal information, and which then connect to Broca's area, especially to area 45. Diffusion tractography indicated connections of PBelt, RI, A4, and A5 with Broca's area 44, and this may be how the dorsal “how” language stream (Rauschecker, 2018; Rauschecker & Scott, 2009) is reflected in the analysis (Rolls, Rauschecker, et al., 2023). Corresponding effective or functional connectivity was not identified in the present analysis, perhaps because it is relatively weak, or perhaps because the data were acquired in the resting state.…”

Lifestyle risks associated with brain functional connectivity and structure

“…A second set of regions with negatively correlated functional connectivities were in the auditory association division, which includes auditory regions A4, A5 and RI, and cortical regions in the superior temporal sulcus (STS) that are involved in semantic representations for language (Rolls, Deco, et al, 2022a ; Rolls, Rauschecker, et al, 2023f ). Other connected language regions (Rolls, Deco, et al, 2022a ; Rolls, Rauschecker, et al, 2023f ) also had negatively correlated functional connectivities, including temporal pole TGd, temporo‐parietal junction TPOJ1, parts of Broca's area 45 and 47l with the connected premotor 55b, and the superior frontal language area (SFL). A third set of regions with connectivities negatively correlated with the combined lifestyle risk score involved the hippocampal memory system and some connected posterior cingulate cortex regions.…”

“…The 30 most significant links are shown in Table S6 . These regions include especially auditory and language‐related STS regions (see Rolls, Deco, et al, 2022a ; Rolls, Rauschecker, et al, 2023f ), including their links with each other and with other cortical regions. The regions with functional connectivities positively correlated with alcohol consumption included links involving 10v in the ventromedial prefrontal cortex and subgenual area 25 (Rolls, Deco, et al, 2023e ).…”

“…A feature of this atlas is that many of the cortical regions can be related to corresponding regions in macaques, which helps complementary neurophysiological investigations to be brought to bear when considering function, as illustrated above. Another feature of this atlas is that the effective connectivity of all 360 cortical regions is starting to be understood, which helps greatly with understanding function (Rolls et al, 2022a ; Rolls, et al, 2023a ; Rolls, et al, 2023b ; Rolls, et al, 2023c ; Rolls, et al, 2023d ; Rolls, et al, 2022b ; Rolls, et al, 2023e ; Rolls, et al, 2023f ; Rolls, et al, 2023g ). A third highlight is that because this HCP‐MMP atlas (Glasser et al, 2016 ; Huang, Rolls, et al, 2022 ) was used, it is possible to consider how the functions of the different cortical areas are related to the different lifestyle choices, helping to elucidate why those lifestyle choices may be made and/or the implications of those lifestyle choices for brain function, as shown above in the Discussion and thereby going beyond a previous investigation (Bittner et al, 2019 ).…”