Objectives: The objective of the proposed study is to determine whether increased activity in right frontal cortex (right pars triangularis) of older persons helps or hinders word retrieval. Research Plan: To accomplish this goal, 1 Hz repetitive transcranial magnetic stimulation (rTMS) will be applied to the experimental area of cortex (right pars triangularis: R PTr) and a control area (right pars opercularis: R POp) in older and younger adults. Sham rTMS also will be applied for purposes of comparison. 1 Hz rTMS has been shown to reduce the excitability of cortex, which interferes with its functions. If increased R PTr activity helps word retrieval for older adults, then 1 Hz rTMS should interfere with their word retrieval and slow picture naming compared to sham rTMS. However, if R PTr activity actually interferes with word retrieval for older persons, as we hypothesize, then lowering its excitability should enhance word retrieval and speed up picture naming compared to sham rTMS. Methods: Sixteen right-handed older adults (65-89 years of age) and 16 right-handed younger adults (20-34 years of age) will perform picture naming during functional magnetic resonance imaging (fMRI) to define areas of peak activity in two right frontal areas: R PTr and R POp. In separate sessions, both groups will receive 10 minutes of 1 Hz rTMS of R PTr and R POp at the locus of peak activity from fMRI. During each session, sham 1 Hz rTMS also will be done. Immediately after both real and sham rTMS, subjects will name 30 pictures, and reaction times for picture naming will be recorded. A priori analyses will be conducted as follows: (1) A repeated-measures t test for both older and younger subjects will assess if there is a significant change in reaction times for picture naming from sham to real rTMS of R PTr. We hypothesize that rTMS will speed up reaction times for older but not younger adults. (2) A repeated-measures t test will assess if there is a significant difference between reaction-time changes from sham to real rTMS for R PTr vs R Pop sessions. Dependent variables will be the change in picture-naming reaction times from sham to real rTMS (real minus sham) for the R PTr and R POp sessions. We hypothesize that reaction times in older adults will speed up for R PTr relative to R POp. Clinical Relevance: This work is clinically relevant in two ways: First, if we can determine the cause of poor word retrieval in older adults, then we can devise an intervention for it in older adults who demonstrate poor word retrieval or who are at risk for it. Such an intervention not only would increase quality of life b enhancing communication, it would reduce the chance of poor health outcomes. Second, patients who have aphasia after left-hemisphere stroke are usually older persons. Knowing how the older brain functions in general will enhance our ability to conceptualize and develop aphasia treatments in stroke survivors.
Of nearly 22 million US veterans, 38.5% are over 65. With an additional 24.9% of veterans between the ages of 55 and 64, the number of veterans over age 65 will increase dramatically in the next decade. Word retrieval in older adults declines from the late 50's through the 90's in independently living, community dwelling adults. Our research indicates that both speed and accuracy of word retrieval are affected in older, community-dwelling adults compared to younger adults. Poor word retrieval affects the ability to communicate. Reduced communication effectiveness can impact quality of life and put older adults at risk for inaccurate diagnosis and poor health outcomes. Our study will determine whether greater right frontal activity in older compared to younger adults helps or hurts word finding. Eventually, this information can be used to develop interventions for poor word finding in older adults at risk for poor communication, impacting quality of life and health outcomes for millions of veterans.
