Regional networks underlying interhemispheric connectivity: an EEG and DTI study in healthy ageing and amnestic mild cognitive impairment

Abstract

Interhemispheric coherence derived from electroencephalogram (EEG) recordings is a measure of functional interhemispheric connectivity. Diffusion tensor imaging (DTI) determines the integrity of subcortical fiber tracts. We studied the pattern of subcortical fiber tracts underlying interhemispheric coherence and its alteration in 16 subjects with amnestic mild cognitive impairment (MCI), an at risk syndrome for Alzheimer's disease, and 20 cognitively healthy elderly control subjects using resting state EEG and high resolution DTI at 3 T. We used a multivariate network approach based on principal component analysis to determine effects of coherence on the regional pattern of diffusivity. Temporo-parietal coherence in the alpha band was significantly correlated with diffusivity in predominantly posterior white matter tracts including posterior corpus callosum, parietal, temporal and occipital lobe white matter, thalamus, midbrain, pons, and cerebellum, both in MCI subjects and controls (P < 0.05). In MCI subjects, frontal coherence in the alpha band was significantly correlated with a predominately frontal pattern of diffusivity including fiber tracts of the anterior corpus callosum, frontal lobe white matter, thalamus, pons, and cerebellum (P < 0.05). The study provides a methodology to access specific networks of subcortical fiber tracts subserving the maintenance of interhemispheric resting state coherence in the human brain.

Figure 1

Projection of the negative components of the canonical image into voxel space‐posterior and frontal coherence in MCI patients, FA maps. (a) Axial sections: The canonical images derived from the FA maps for posterior and frontal coherence, respectively, in MCI patients in voxel space projected on the rendered axial sections of the T1‐weighted template brain. Sections move from dorsal at Talairach–Tournoux coordinate z = 57 to ventral z = −35, sections are 4 mm apart. Right of image is right of brain (view from superior). L – left. (b) Midsagittal section: red to yellow: components of the canonical image for temporo‐parietal coherence. Blue to green: components of the canonical images for frontal coherence.

Figure 2

Projection of the negative components of the canonical image into voxel space ‐temporo‐parietal coherence in healthy controls, FA maps. (a) Axial sections: The canonical images derived from the FA maps for temporo‐parietal coherence in healthy control subjects in voxel space projected on the rendered axial sections of the T1‐weighted template brain. Sections move from dorsal at Talairach–Tournoux coordinate z = 57 to ventral z = −35, sections are 4 mm apart. Right of image is right of brain (view from superior). L, left. (b) Midsagittal section.

Figure 3

Projection of the positive components of the canonical image into voxel space ‐temporo‐parietal and frontal coherence in MCI patients, MD maps. (a) Axial sections: The canonical images derived from the MD maps for posterior and frontal coherence, respectively, in MCI patients in voxel space projected on the rendered axial sections of the T1‐weighted template brain. Sections move from dorsal at Talairach–Tournoux coordinate z = 57 to ventral z = −35, sections are 4 mm apart. Right of image is right of brain (view from superior). L, left. (b) Midsagittal section: red to yellow: components of the canonical image for temporo‐parietal coherence. Blue to green: components of the canonical images for frontal coherence.

Figure 4

Projection of the positive components of the canonical image into voxel space ‐temporo‐parietal coherence in controls, MD maps. (a) Axial sections: The canonical images derived from the MD maps for temporo‐parietal coherence in healthy control subjects in voxel space projected on the rendered axial sections of the T1‐weighted template brain. Sections move from dorsal at Talairach‐Tournoux coordinate z = 57 to ventral z = −35, sections are 4 mm apart. Right of image is right of brain (view from superior). L, left. (b) Midsagittal section.