12 Alzheimer’s disease, memory, and fMRI

Alzheimer’s disease (AD) is a neurological disorder characterized by the gradual impairment of various cognitive domains, including short-term and episodic memory. AD is also the most prevalent type of dementia. Short-term memory (STM) is a cognitive domain affected by AD (Huntley et al., 2017). This cognitive domain stores a small amount of information for a brief interval of time (approximately 30 seconds).

Conjunctive STM binding tests evaluate one’s ability to mentally hold conjunctions between surface features in relation to one’s ability to hold the individual features (Cecchini et al., 2022). A meta-analysis and systematic review of 20 studies that used conjunctive STM binding tests with individuals in either preclinical cognitive decline, mild cognitive impairment (MCI), or dementia revealed large effects in all AD stages. The meta-analysis suggests that those with dementia struggle much more to hold conjunctions of information (i.e., an item’s color and shape) significantly more than individual features. Participants with MCI significantly struggled to temporarily hold both individual features and conjunctions of information. The meta-analysis also revealed difficulty holding conjunctions of information, but not individual features in those with preclinical cognitive decline. To summarize, the systematic review provided evidence of difficulty holding conjunctions of information in STM in AD continuum patients, even at the preclinical cognitive decline stage.

Functional magnetic resonance imaging (fMRI) results show decreased functional activity in the left parietal cortex (LPC), right parietal cortex (RPC), left dorsolateral prefrontal cortex (DLPFC), and right DLPFC in early AD patients following chunking-based cognitive training (Huntley et al., 2017). Chunking-based cognitive training is defined as using theoretically motivated exercises targeting certain cognitive domains to enhance cognitive function. To successfully complete a task, large executive and attentional resources might initially be required. These resources might be underpinned by cortical regions of interest (ROIs), such as the posterior parietal cortex (PPC) and PFC. As early AD patients continue chunking-based cognitive training, the need for executive and attentional resources is reduced. This explains the decrease in functional activity shown on fMRI scans. Chunking-based cognitive training also results in significant improvement in STM. The study provides evidence of functional plasticity following chunking-based cognitive training during early onset of AD.