title: Somatosensory responses in normal aging, mild cognitive impairment, and Alzheimer's disease.
abstract: As a part of a larger study of normal aging and Alzheimer's disease (AD), which included patients with mild cognitive impairment (MCI), we investigated the response to median nerve stimulation in primary and secondary somatosensory areas. We hypothesized that the somatosensory response would be relatively spared given the reported late involvement of sensory areas in the progression of AD. We applied brief pulses of electric current to left and right median nerves to test the somatosensory response in normal elderly (NE), MCI, and AD. MEG responses were measured and were analyzed with a semi-automated source localization algorithm to characterize source locations and timecourses. We found an overall difference in the amplitude of the response of the primary somatosensory source (SI) based on diagnosis. Across the first three peaks of the SI response, the MCI patients exhibited a larger amplitude response than the NE and AD groups (P < 0.03). Additional relationships between neuropsychological measures and SI amplitude were also determined. There was no significant difference in amplitude for the contralateral secondary somatosensory source across diagnostic category. These results suggest that somatosensory cortex is affected early in the progression of AD and may have some consequence on behavioral and functional measures.
authors.affiliation: The Mind Research Network, 1101 Yale Boulevard NE, Albuquerque, NM 87106, USA. jstephen@mrn.org
authors.forename: Julia M
authors.initials: JM
authors.lastname: Stephen
authors.forename: Rebecca
authors.initials: R
authors.lastname: Montaño
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Donahue
authors.forename: John C
authors.initials: JC
authors.lastname: Adair
authors.forename: Janice
authors.initials: J
authors.lastname: Knoefel
authors.forename: Clifford
authors.initials: C
authors.lastname: Qualls
authors.forename: Blaine
authors.initials: B
authors.lastname: Hart
authors.forename: Doug
authors.initials: D
authors.lastname: Ranken
authors.forename: Cheryl J
authors.initials: CJ
authors.lastname: Aine
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D000465:Algorithms; D000544:Alzheimer Disease / Q000503:physiopathology*; D001331:Automation; D003072:Cognition Disorders / Q000503:physiopathology*; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008475:Median Nerve / Q000503:physiopathology; D008875:Middle Aged; D009483:Neuropsychological Tests; D012815:Signal Processing, Computer-Assisted; D013003:Somatosensory Cortex / Q000503:physiopathology*; D013997:Time Factors; D055698:Touch Perception / Q000502:physiology*