Evidence of neuronal compensation during episodic memory in subjective memory impairment.

CONTEXT: Accumulating evidence suggests that the mere subjective feeling of memory impairment in the absence of objective cognitive deficits may precede mild cognitive impairment in the continuum of Alzheimer disease manifestation. Brain imaging studies have provided insights into structural and functional alterations at the clinical stages of dementia and mild cognitive impairment, but the functional characteristics of subjective memory impairment (SMI) are largely unstudied.
OBJECTIVE: To investigate brain activation during memory tasks in individuals without cognitive impairment who report SMI compared with control subjects without cognitive impairment and without SMI.
DESIGN: Functional magnetic resonance imaging study of episodic memory and working memory.
SETTING: Memory outpatient clinic. PARTICIPANTS: Nineteen participants reporting SMI without cognitive impairment and 20 control individuals without cognitive impairment and SMI. MAIN OUTCOME MEASURE: Brain activation patterns and performance during an associative face-profession episodic memory task, including encoding, recall, and recognition, and a working memory task.
RESULTS: Compared with the control group, SMI was associated with a reduction in right hippocampal activation during episodic memory recall in the absence of performance deficits. This was accompanied by increased activation of the right dorsolateral prefrontal cortex. No differences in performance and no difference in brain activation during working memory were observed in the SMI group.
CONCLUSIONS: These results suggest that SMI is accompanied by functional alterations in hippocampal integrity that reflect early neuronal dysfunction and by compensatory mechanisms that preserve memory performance.