The Associative Memory Deficit in Aging Is Related to Reduced Selectivity of Brain Activity during Encoding

Abstract

Human aging is characterized by reductions in the ability to remember associations between items, despite intact memory for single items. Older adults also show less selectivity in task-related brain activity, such that patterns of activation become less distinct across multiple experimental tasks. This reduced selectivity or dedifferentiation has been found for episodic memory, which is often reduced in older adults, but not for semantic memory, which is maintained with age. We used fMRI to investigate whether there is a specific reduction in selectivity of brain activity during associative encoding in older adults, but not during item encoding, and whether this reduction predicts associative memory performance. Healthy young and older adults were scanned while performing an incidental encoding task for pictures of objects and houses under item or associative instructions. An old/new recognition test was administered outside the scanner. We used agnostic canonical variates analysis and split-half resampling to detect whole-brain patterns of activation that predicted item versus associative encoding for stimuli that were later correctly recognized. Older adults had poorer memory for associations than did younger adults, whereas item memory was comparable across groups. Associative encoding trials, but not item encoding trials, were predicted less successfully in older compared with young adults, indicating less distinct patterns of associative-related activity in the older group. Importantly, higher probability of predicting associative encoding trials was related to better associative memory after accounting for age and performance on a battery of neuropsychological tests. These results provide evidence that neural distinctiveness at encoding supports associative memory and that a specific reduction of selectivity in neural recruitment underlies age differences in associative memory.

Brain reserve, cognitive reserve, compensation, and maintenance: operationalization, validity, and mechanisms of cognitive resilience

“…On average, older adults remember these paired stimuli more poorly than do younger adults. When the tests are administered as a part of a functional MRI (fMRI) experiment, older participants show reduced selectivity in brain regions that are specifically involved in encoding the paired images (Saverino et al, 2016), consistent with their reduced associative memory. This provides evidence that reduced selectivity (dedifferentiation) of brain activity during encoding, one type of dynamic brain activity, may be an important mechanism underlying reduced memory performance in older adults.…”

Incidental Learning: A Systematic Review of Its Effect on Episodic Memory Performance in Older Age

“…Saverino et al (2016) found similar activity in the right middle occipital gyrus and the left parahippocampus in both groups during encoding of house pictures. For incidental associative encoding of objects, elderly adults exhibited decreased activity in the inferior frontal gyrus, the left precuneus, the right inferior temporal gyrus, and the left middle as well as the right posterior cingulate cortex.…”

“…Saverino et al (2016) tested item and associative encoding under incidental conditions. For item encoding, participants indicated if the style of a given house on a picture was modern or traditional.…”

Accelerated intermittent theta-burst stimulation broadly ameliorates symptoms and cognition in Alzheimer's disease: A randomized controlled trial

“…Loss of associative memory (AM), which is the binding of contextual information to stimulus attributes, is commonly considered an early and prominent feature of AD [7]. Measures of AM, which are most vulnerable to AD's pathological processes, are correlated with cerebrospinal fluid markers of AD neurodegeneration [8].…”