Verbal Memory in Parkinson's Disease: A Combined DTI and fMRI Study

Abstract

Background: While significant progress has been made to determine the functional role of specific gray matter areas underlying verbal memory in Parkinson's disease (PD), very little is known about the relationship between these regions and their underlying white matter structures.

Objective: The objectives of this study were (1) to investigate verbal memory, fractional anisotropy and brain activation differences between PD patients and healthy controls (HC), (2) to explore the neuroanatomical and neurofunctional correlates of verbal memory in PD, and (3) to investigate the relationship between these neuroanatomical and neurofunctional verbal memory correlates in PD.

Methods: Functional magnetic resonance imaging (fMRI) while performing a verbal memory paradigm and diffusion tensor imaging data (DTI), were acquired in 37 PD patients and 15 age-, sex-, and education-matched HC.

Results: PD patients showed verbal recognition memory impairment, lower fractional anisotropy in the anterior cingulate tract, and lower brain activation in the inferior orbitofrontal cortex compared to HC. Brain activation in the inferior orbitofrontal cortex correlated significantly with verbal recognition memory impairment in PD patients. In addition, a relationship between brain activation in the inferior orbitofrontal cortex and fractional anisotropy of the uncinate fasciculus was found in PD.

Conclusions: These results reveal that deficits in verbal memory in PD are accompanied by functional brain activation changes, but also have specific structural correlates related to white matter microstructural integrity.

Fig.1

Regions of Interest of WM FA tracts. Montreal Neurological Institutes (MNI) template coordinates based on JHU WM Tractography Atlas. WM = White Matter; FA = Fractional Anisotropy; L = Left; R = Right; ACT = Anterior Cingulate Tract; PCT = Posterior Cingulate Tract; UF = Uncinate Fasciculus.

Fig.2

Regions of Interest of fMRI brain activation in axial, coronal and sagittal view. Montreal Neurological Institutes (MNI) template coordinates for a): x = –50.2 y = –40.8 z = –13.5. MNI for b): x = 53.7 y = 31 z = –12.5. L = Left; R = Right; MTL = Medial Temporal Lobe; IOFC = Inferior Orbitofrontal Cortex.

Fig.3

Significant voxel-wise correlations (red) between fractional anisotropy (FA) of the right uncinate fasciculus (UF) and brain activation in the left orbitofrontal cortex (IOFC) during verbal learning memory fMRI task. Montreal Neurological Institutes (MNI) template coordinates: x = 36 y = –5 z = 18.