Functional connectivity and alterations in baseline brain state in humans

Abstract

This work examines the influence of changes in baseline activity on the intrinsic functional connectivity fMRI (fc-fMRI) in humans. Baseline brain activity was altered by inducing anesthesia (sevoflurane end-tidal concentration 1%) in human volunteers and fc-fMRI maps between the pre-anesthetized and anesthetized conditions were compared across different brain networks. We particularly focused on low-level sensory areas (primary somatosensory, visual, and auditory cortices), the thalamus, and pain (insula), memory (hippocampus) circuits, and the default mode network (DMN), the latter three to examine higher-order brain regions. The results indicate that, while fc-fMRI patterns did not significantly differ (p<0.005; 20-voxel cluster threshold) in sensory cortex and in the DMN between the pre- and anesthetized conditions, fc-fMRI in high-order cognitive regions (i.e. memory and pain circuits) was significantly altered by anesthesia. These findings provide further evidence that fc-fMRI reflects intrinsic brain properties, while also demonstrating that 0.5 MAC sevoflurane anesthesia preferentially modulates higher-order connections.

Figure 1

Significant fc-fMRI values relative to the left BA 1 seed region, under the pre-, post-, and anesthesia conditions (A) and the contrast between anesthesia and pre-anesthesia (B) within different axial slices shown in radiological convention (MNI z-coordinates reported in the inset), or in a three-dimensional reconstruction of the template brain (C). Colors represent fc-fMRI significance, reported as T values. Anesthesia increased connectivity with the thalamus and primary motor/somatosensory areas, and reduced the connectivity with extrastriate visual areas.

Figure 2

Significant fc-fMRI values relative to the left BA 17 seed region, under the pre-, post-, and anesthesia conditions (A) and the contrast between anesthesia and pre-anesthesia (B) within different axial slices shown in radiological convention (MNI z-coordinates reported in the inset), or in a three-dimensional reconstruction of the template brain (C). Colors represent fc-fMRI significance, reported as T values. High-order visual areas showed an increased connectivity with BA 17 under anesthesia.

Figure 3

Significant fc-fMRI values relative to the left Heschel’s gyrus seed region, under the pre-, post-, and anesthesia conditions (A) and the contrast between anesthesia and pre-anesthesia (B) within different axial slices shown in radiological convention (MNI z-coordinates reported in the inset), or in a three-dimensional reconstruction of the template brain (C). Colors represent fc-fMRI significance, reported as T values. Anesthesia increased the connectivity of the Heschel’s gyrus with the thalamus and the right STS.

Figure 4

Significant fc-fMRI values relative to the left thalamus seed region, under the pre-, post-, and anesthesia conditions (A) and the contrast between anesthesia and pre-anesthesia (B) within different axial slices shown in radiological convention (MNI z-coordinates reported in the inset), or in a three-dimensional reconstruction of the template brain (C). Colors represent fc-fMRI significance, reported as T values. Under anesthesia, thalamus showed a stronger connectivity with SMA and insula, while connectivity with the caudate and left IPL was decreased.

Figure 5

Significant fc-fMRI values relative to the left hippocampus seed region, under the pre-, post-, and anesthesia conditions (A) and the contrast between anesthesia and pre-anesthesia (B) within different axial slices shown in radiological convention (MNI z-coordinates reported in the inset), or in a three-dimensional reconstruction of the template brain (C). Colors represent fc-fMRI significance, reported as T values. Connectivity between hippocampus and PCC and IPL was reduced by anesthesia.

Figure 6

Significant fc-fMRI values relative to the left insula seed region, under the pre-, post-, and anesthesia conditions (A) and the contrast between anesthesia and pre-anesthesia (B) within different axial slices shown in radiological convention (MNI z-coordinates reported in the inset), or in a three-dimensional reconstruction of the template brain (C). Colors represent fc-fMRI significance, reported as T values. Under anesthesia, connectivity with bilateral SII and with left middle frontal gyrus was reduced.

Figure 7

Significant fc-fMRI values relative to the PCC seed region, under the pre-, post-, and anesthesia conditions (A) and the contrast between anesthesia and pre-anesthesia (B) within different axial slices shown in radiological convention (MNI z-coordinates reported in the inset), or in a three-dimensional reconstruction of the template brain (C). Colors represent fc-fMRI significance, reported as T values. Anesthesia increased the connectivity between PCC and STG and reduced connectivity with areas adjacent to the seed region.