The Relationship between Age, Neural Differentiation, and Memory Performance

Abstract

Healthy aging is associated with decreased neural selectivity (dedifferentiation) in category-selective cortical regions. This finding has prompted the suggestion that dedifferentiation contributes to age-related cognitive decline. Consistent with this possibility, dedifferentiation has been reported to negatively correlate with fluid intelligence in older adults. Here, we examined whether dedifferentiation is associated with performance in another cognitive domain-episodic memory-that is also highly vulnerable to aging. Given the proposed role of dedifferentiation in age-related cognitive decline, we predicted there would be a stronger link between dedifferentiation and episodic memory performance in older than in younger adults. Young (18-30 years) and older (64-75 years) male and female humans underwent fMRI scanning while viewing images of objects and scenes before a subsequent recognition memory test. We computed a differentiation index in two regions of interest (ROIs): parahippocampal place area (PPA) and lateral occipital complex (LOC). This index quantified the selectivity of the BOLD response to preferred versus nonpreferred category of an ROI (scenes for PPA, objects for LOC). The differentiation index in the PPA, but not the LOC, was lower in older than in younger adults. Additionally, the PPA differentiation index predicted recognition memory performance for the studied items. This relationship was independent of and not moderated by age. The PPA differentiation index also predicted performance on a latent "fluency" factor derived from a neuropsychological test battery; this relationship was also age invariant. These findings suggest that two independent factors, one associated with age, and the other with cognitive performance, influence neural differentiation.

Memory specificity is linked to repetition effects in event-related potentials across the lifespan

“…In line with this, it has been suggested that neural representations become less specific in old age, which may be linked to aging-related cognitive decline (Carp et al, 2011;Li and Sikström, 2002;Li et al, 2001;Park et al, 2004Park et al, , 2010. Indeed, a positive relation between the specificity of the neural activity patterns during encoding and memory performance could be demonstrated for young and older adults (Kobelt et al, 2020;Koen et al, 2019). In children (7-12 years), higher neural specificity of scene representations was associated with better memory performance, too (Fandakova et al, 2019).…”

Effects of Aging on the Encoding of Spatial Direction in the Human Brain

“…Since there was no group difference in classification accuracy in the RSC, it remains unclear if this process is connected specifically to the aging brain or rather describes a process which is happening throughout the adult lifespan (Rugg, 2016). This idea was also supported by a study by Koen et al (2018) where the connection between neural dedifferentiation and memory performance was also age invariant.…”

“…To the best of our knowledge, this is the first study to investigate potential age-related changes in tuning functions defined over a continuous domain, rather than using discrete categories (J. Park et al, 2012; Koen et al, 2019). This is a notable distinction from previous research since mechanisms of age-related changes are likely different in these two cases: dedifferentiated responses within local circuits, which code the same continuous quantity, are related to changes in local inhibitory control, such as GABAergic interneurons (Leventhal et al, 2003); cross-areal dedifferentiation conceivably reflects a range of different mechanisms, including changes in long range connectivity or task strategies (Reuter-Lorenz & Lustig, 2005; Reuter-Lorenz & Cappell, 2008).…”

“…D. C. Park et al, 2004; Voss et al, 2008; Burianová, Lee, Grady, & Moscovitch, 2013; Carp et al, 2011). Neural dedifferentiation has also been linked to memory impairment with older age (Zheng et al, 2018; Koen, Hauck, & Rugg, 2019) and related changes to similarity of neural representations might play a crucial role in the encoding and retrieval of memory content (Koen, Hauck, & Rugg, 2018; Sommer et al, 2019). Moreover, electrophysiological recordings in V1 of senescent Rhesus monkeys have found that tuning curves of orientation responsive neural populations broaden with age, effectively widening the spectrum of orientation angles a single neuron responds to (Leventhal, Wang, Pu, Zhou, & Ma, 2003; Schmolesky et al, 2000).…”

Network models predict that pyramidal neuron hyperexcitability and synapse loss in the dlPFC lead to age-related spatial working memory impairment in rhesus monkeys

“…Such units could be well-suited for extending the DRSTsp model introduced here to simulate choice of the novel spatial cue and related internal signals, plus the full 3x6 array of wells presented to the monkeys during the DRSTsp. There is evidence that aging affects information flow between cortical regions, which can contribute to working memory impairment (Engle et al, 2016;Lee et al, 2016;Proskovec et al, 2016;King et al, 2018;Koen et al, 2019). Any such age effects must be examined in concert with the changes to dlPFC synapses and neuronal excitability, to predict the extent to which these concomitant changes compound versus partially compensate each other.…”