Flexible modulation of network connectivity related to cognition in Alzheimer's disease.
Functional neuroimaging tools, such as fMRI methods, may elucidate the neural correlates of clinical, behavioral, and cognitive performance. Most functional imaging studies focus on regional task-related activity or resting state connectivity rather than how changes in functional connectivity across conditions and tasks are related to cognitive and behavioral performance. To investigate the promise of characterizing context-dependent connectivity-behavior relationships, this study applies the method of generalized psychophysiological interactions (gPPI) to assess the patterns of associative-memory-related fMRI hippocampal functional connectivity in Alzheimer's disease (AD) associated with performance on memory and other cognitively demanding neuropsychological tests and clinical measures. Twenty-four subjects with mild AD dementia (ages 54-82, nine females) participated in a face-name paired-associate encoding memory study. Generalized PPI analysis was used to estimate the connectivity between the hippocampus and the whole brain during encoding. The difference in hippocampal-whole brain connectivity between encoding novel and encoding repeated face-name pairs was used in multiple-regression analyses as an independent predictor for 10 behavioral, neuropsychological and clinical tests. The analysis revealed connectivity-behavior relationships that were distributed, dynamically overlapping, and task-specific within and across intrinsic networks; hippocampal-whole brain connectivity-behavior relationships were not isolated to single networks, but spanned multiple brain networks. Importantly, these spatially distributed performance patterns were unique for each measure. In general, out-of-network behavioral associations with encoding novel greater than repeated face-name pairs hippocampal-connectivity were observed in the default-mode network, while correlations with encoding repeated greater than novel face-name pairs hippocampal-connectivity were observed in the executive control network (p<0.05, cluster corrected). Psychophysiological interactions revealed significantly more extensive and robust associations between paired-associate encoding task-dependent hippocampal-whole brain connectivity and performance on memory and behavioral/clinical measures than previously revealed by standard activity-behavior analysis. Compared to resting state and task-activation methods, gPPI analyses may be more sensitive to reveal additional complementary information regarding subtle within- and between-network relations. The patterns of robust correlations between hippocampal-whole brain connectivity and behavioral measures identified here suggest that there are 'coordinated states' in the brain; that the dynamic range of these states is related to behavior and cognition; and that these states can be observed and quantified, even in individuals with mild AD.
Department of Neurology, Massachusetts General Hospital, 15 Parkman Street, WACC 715, Boston, MA 02114, USA; Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, 149 Thirteenth Street, Charlestown, MA 02129, USA; Geriatric Research, Education and Clinical Center, ENRM VA Medical Center, 200 Springs Road, Bedford, MA 01730, USA; Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA. Electronic address: dmclaren2@partners.org.
Donald G
DG
McLaren
Department of Neurology, Massachusetts General Hospital, 15 Parkman Street, WACC 715, Boston, MA 02114, USA; Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, 149 Thirteenth Street, Charlestown, MA 02129, USA; Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA; Center for Alzheimer Research and Treatment, Department of Neurology, Brigham and Women's Hospital, 221 Longwood Avenue, Boston, MA 02115, USA. Electronic address: rsperling@rics.bwh.harvard.edu.
Reisa A
RA
Sperling
Department of Neurology, Massachusetts General Hospital, 15 Parkman Street, WACC 715, Boston, MA 02114, USA; Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, 149 Thirteenth Street, Charlestown, MA 02129, USA; Geriatric Research, Education and Clinical Center, ENRM VA Medical Center, 200 Springs Road, Bedford, MA 01730, USA; Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA. Electronic address: atri@nmr.mgh.harvard.edu.
Alireza
A
Atri
D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000503:physiopathology*; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D005260:Female; D006624:Hippocampus / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D061212:Memory, Episodic; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology*
Biomarker; Dementia; Episodic memory; Functional MRI; Functional connectivity; gPPI