Brainwide mesoscale functional networks revealed by focal infrared neural stimulation of the amygdala

Abstract

The primate amygdala serves to evaluate the emotional content of sensory inputs and modulate emotional and social behaviors; it modulates cognitive, multisensory and autonomic circuits predominantly via the basal, lateral and central nuclei, respectively. Recent evidence has suggested the mesoscale (millimeter-scale) nature of intra-amygdala functional organization. However, the connectivity patterns by which these mesoscale regions interact with brainwide networks remain unclear. Using infrared neural stimulation of single mesoscale sites coupled with mapping in ultrahigh field 7-T functional magnetic resonance imaging, we have discovered that these mesoscale sites exert influence over a surprisingly extensive scope of the brain. Our findings strongly indicate that mesoscale sites within the amygdala modulate brainwide networks through a 'one-to-many' (integral) way. Meanwhile, these connections exhibit a point-to-point (focal) topography. Our work provides new insights into the functional architecture underlying emotional and social behavioral networks, thereby opening up possibilities for individualized modulation of psychological disorders.

Keywords: amygdala; brainwide network; connectional topography; infrared neural stimulation; intra-individual datasets; mesoscale topography; ultrahigh field fMRI.

Figure 1.

Possible mesoscale connectivity patterns. Colored circles: mesoscale domains. Areas surrounded by dashed lines: brain areas.

Figure 2.

Identifying functionally connected sites in the brain following INS stimulation of single mesoscale sites in the amygdala. (A) A coronal section through the caudal amygdala. (B) Parcellation of the amygdala at the most caudal site shown in (A). CeA: central amygdala; AB: accessory basal amygdala; BA: basal amygdala; LA: lateral amygdala; Hipp: hippocampus. (C) Raw structural image indicating the optical fiber inserted through a grid in a chamber. (D) Activation at the laser tip in CeA (red voxel, intensity: 0.2 J/cm², P < 1 × 10^–6). (E) BOLD timecourse at the laser tip in D (TR = 2000 ms). Above: 15 consecutive trials; below: averaged timecourse (the dotted rectangle spans the duration of INS). Each red line: one trial of four pulse trains (see Methods). (F–H) Coronal, sagittal and horizontal view of a remote cluster activated in response to stimulation in (D) (P < 1 × 10^–4). (I) Activation cluster (white arrow) in (F–H) shown on inflated brain surface. (J) BOLD timecourse at connected cluster (white arrow) in (f–h). Above: all 15 trials; below: averaged timecourse.

Figure 3.

Mesoscale brainwide connections of the amygdala. (A) The white dots represent the INS stimulation sites in the right amygdala. CeA (green contour, six sites), BA (yellow contour, three sites), LA (red contour, three sites). LA: lateral amygdala; BA: basal amygdala; AB: accessory basal amygdala; CeA: central amygdala; MeA: medial amygdala; ICA: intercalated cell masses; AAA: anterior amygdala area. (B) The stacked histogram for patch size of brainwide cortical activations. The x axis represents the size of patches in millimeters squared. The y axis represents the number of patches of different sizes. Each color represents a stimulation site in monkey K, namely six sites in CeA (upper row, shades of green), three sites in BA (middle row, shades of yellow) and three sites in LA (lower row, shades of red). (C) Whole-brain activations evoked by single stimulation sites (one site for each of CeA, BA and LA) mapped on inflated hemisphere (ipsilateral to the stimulation) of monkey K and monkey M. Both medial view and lateral view are presented. Ps: principal sulcus; As: arcuate sulcus; Cs: central sulcus; IPs: intraparietal sulcus; syf: sylvian fissure; sts: superior temporal sulcus; Ls: lunate sulcus; IOs: inferior occipital sulcus; Cgs: cingulate sulcus; POs: parietal-occipital sulcus; POm: medial parieto-occipital sulcus; calc: calcarine.

Figure 4.

Cortical distributions of CeA, BA and LA networks. (A) A comparison of connectivity revealed by INS-fMRI and by anatomical tracers. Upper six rows: red represents the presence of functional connections in monkey K and monkey M. Lower six rows: blue represents the combined results of anatomical connections originating from the amygdala and anatomical connections to the amygdala originating from the cortex (based on http://cocomac.g-node.org, see Methods). T.: visual system (temporal); Vis. P.: visual system (parietal); Vis. O.: visual system (occipital); Som.: somatosensory cortex; Lat-PFC: lateral prefrontal cortex; Par.: parietal cortex; OFC: orbital frontal cortex; Mot.: motor cortex; Aud.: auditory cortex; Pi: parainsula; Ig: granular insula; Id: dysgranular insula; Ia: agranular insula. (B and C) Jaccard similarity and cosine similarity between functional connectivity (FC) and anatomical connectivity (AC); the red color represents similarity between FC and AC to the amygdala originating from the cortex, the blue color represents similarity between FC and AC that originated from the amygdala. Results are from two monkeys (monkey K and monkey M), and from stimulation sites out of the amygdala (missed) in monkey K. (D) Proportional composition of cortical connections from CeA, BA and LA in monkey K (e.g. for all stimulation sites in CeA, the # voxels in an area connected to CeA/total voxels connected to CeA). (E) Global distribution of activation evoked by different stimulation sites. Each column illustrates activation from a single site (six in CeA, three in BA, three in LA). The colors represent that the brain areas have outstanding and consistent activations from stimulating sites in CeA (green), BA (yellow) and LA (magenta). The blue color represents that all stimulation sites evoke activations in this brain area. The size of bubbles represents the number of voxels evoked by each stimulation site in each brain area. The numbers were scaled by each stimulation site. (F–H) Summarized global networks involving CeA (F), BA (G) and LA (H), respectively. The colored nodes represent areas dominated by CeA, BA or LA; the white nodes represent areas receiving similar prominence of connections from CeA, BA and LA.

Figure 5.

Functional connections with cingulate cortex, insula and OFC. Topography of connected areas in cingulate cortex (B–E), insula (G–J) and OFC (L-O). Segmentation of the brain areas is shown in the first column (A, F, K). Merged views of CeA, BA and LA are shown in the last column (E, J, O). Iai: intermediate agranular insula; Iapl: posterior lateral agranular insula; Ial: lateral agranular insula. The results are masked by cingulate, insula and OFC for the purpose of highlighting results in these areas.

Figure 6.

Local cortical topography of connections from single amygdala nuclei. Activations from different stimulation sites within each of CeA, BA and LA were mapped onto the cortical surface (P < 1 × 10^–3). (A, D, G) Stimulation sites are shown in 3D coordinates (left) and in rostro-caudal contour cartoons (right). (A–C) Six stimulation sites in CeA revealed connected sites mostly in F1 (B) and FEF Area 8 (C). (D–F) Three stimulation sites in BA revealed connected sites in area V4 (E) and in ventral visual pathway TP, PG, IP, TE (F). (G–I) Three stimulation sites in LA revealed connected sites in auditory belt/parabelt areas AL, ML, CPB, RPB (H) and somatosensory areas 1–2 and SII (I). A1: primary auditory area; R: rostral area; CM: caudomedial belt region; AL: anterolateral belt region; ML: middle lateral belt region; RPB: rostral parabelt region; CPB: caudal parabelt region.

Figure 7.

Connectivity patterns in cortical areas with activations from CeA, BA and LA. Topography of connected sites in V1/V2 (A), SI/SII (B) and area 7 (C), respectively.