according to a small pilot study published online ahead of print April 17 in Neurology. Stimulation also increased functional MRI signals associated with recollection throughout the hippocampal-cortical network.
“Disruption and abnormal functioning of the hippocampal-cortical network, the region of the brain involved in memory formation, has been linked to age-related memory decline, so it’s exciting to see that, by targeting this region, magnetic stimulation may help improve memory in older adults,” said Joel L. Voss, PhD, of Northwestern University in Chicago. “These results may help us better understand how this network supports memory.”
Recollection is the type of memory most impaired during normal aging. Other types of memory, such as recognition, are relatively spared. Research indicates that multiple sessions of TMS improve recollection and hippocampal-cortical network function in young adults.
Dr. Voss and colleagues performed a pilot study to evaluate whether TMS could improve recollection in older adults. They enrolled 15 cognitively normal older adults (mean age, 72.46 years) into a sham-controlled, single-blind, counterbalanced experiment. Eleven subjects were women. Participants underwent fMRI while learning objects paired with scenes and locations. Investigators administered TMS to lateral parietal locations that were based on each participant’s fMRI connectivity with the hippocampus. Using a within-subjects crossover design, Dr. Voss’s group assessed participants’ recollection and recognition memory at baseline and 24 hours and also 1 week after five consecutive daily sessions of full-intensity stimulation, compared with low-intensity sham stimulation.
At baseline, participants had impaired recollection, but not impaired recognition, compared with a historical sample of younger adults. At 24 hours, TMS provided robust recollection improvement and weak recognition improvement, compared with sham. TMS improved recollection by 31.1% from baseline, and sham yielded a nonsignificant change of −3.1%. Recollection improvements after TMS were consistent across participants. Recognition changed by a nonsignificant 2.8% following TMS and by a nonsignificant −2.9% following sham.
The investigators also found a significant and consistent increase in fMRI recollection activity for the targeted hippocampal-cortical network, but not for the control frontal-parietal network. They observed no increased fMRI activity for recognition.
“These findings demonstrate a causal link between recollection and the hippocampal-cortical network in older adults,” said Dr. Voss. “While our small study examined age-related memory loss, it did not examine this stimulation in people with memory loss from more serious conditions such as mild cognitive impairment or Alzheimer’s disease.” Furthermore, the study was designed to test for neural and behavioral target engagement, but not clinical efficacy, he added.
The study’s limitations included its small sample size, its single-site design, and its lack of active control stimulation. Nevertheless, it identified specific and consistent effects of stimulation across participants that were consistent with previous findings in younger adults. “These findings motivate future studies to optimize the effectiveness of noninvasive stimulation for treatment of age-related memory impairment and to improve mechanistic understanding of the hippocampal-cortical networks that support episodic memory across the lifespan,” said Dr. Voss.
The National Institute on Aging, as well as the Northwestern University Cognitive Neurology and Alzheimer’s Disease Center, supported the study.
SOURCE: Nilakantan AS et al. Neurology. 2019 Apr 17 doi: 10.1212/WNL.0000000000007502.