Rethinking the neuroanatomical organization of cognition: Recognition memory in visual cortex - PROJECT SUMMARY
By 2035, the number of US residents over 65 years will surpass the number under the age of 35 years, totaling
20% of the US population. Meanwhile, by 2050 the world population is projected to increase by 17%, to include
1.6 billion people aged 65 or older. Progressive deficits in memory are a common fact of aging, in addition to
being a primary symptom of Alzheimer's disease. Yet, treatments for memory disorders such as seen in aging
and Alzheimer's are limited. One obstacle is that we still have not attained a thorough understanding of how
brain systems are functionally organized to produce memory in the healthy brain. Based on case studies like
patient H.M., traditional accounts of cognition explain memory and perception in terms of processes computed
by separable brain regions (or distinct brain networks). In contrast, the Representational-Hierarchical (R-H)
account posits that a brain region can be engaged in any cognitive task, if it contains optimal representations for
solving the task. The specific objective of this proposal is to test my overarching hypothesis that brain
regions contribute to a cognitive task – be it perceptual or mnemonic – according to the representations
they contain. The R-H Theory postulates that the organization of cognition (i.e., memory and perception) in the
brain is better understood in terms of a hierarchical continuum of representations, as opposed to anatomical
modules (or circumscribed "networks") for distinct cognitive processes like "episodic memory". The central
hypothesis of this proposal is that declarative memory may be computed in sensory cortex without involving the
medial temporal lobe (MTL). Aim 1 will determine whether recognition memory can be supported by
structures outside of canonical memory regions (i.e., MTL), in brain areas known to mediate perception
(e.g., visual cortex). In this fMRI study, I will test participants' (long-term, declarative) recognition memory for
stimuli they have studied. I hypothesize that if to-be-remembered items are abstract visual objects comprising
conjunctions of visual features, and if the task requires recognition of familiar versus novel conjunctions of
features, then the brain regions supporting memory will fall outside of MTL, in visual cortical sites such as lateral
occipital cortex. Aim 2 will test whether aging (associated with incipient MTL deterioration) leads to greater
deficits in recognition memory for high-level associative stimuli than for low-level visual stimuli. I will
use the visual stimuli from Aim 1, along with analogously constructed word-pair stimuli. We assume that MTL
networks deteriorate in aging. My working hypothesis, derived from the R-H Theory, is that older adults will
perform worse for word pairs than visual stimuli, relative to younger adults, because word-pairs (but not visual
stimuli) require high-level representations, which are MTL-dependent. This proposal has translational and
theoretical significance. The results will determine whether the R-H Theory provides a better explanation of
how human brains give rise to cognition. Both aims may lay the groundwork for improved diagnosis and treatment
of memory disorders in aging and Alzheimer's, potentially alleviating patient suffering and familial burdens.