Visual Personal Familiarity in Amnestic Mild Cognitive Impairment

BACKGROUND: Patients with amnestic mild cognitive impairment are at high risk for developing Alzheimer's disease. Besides episodic memory dysfunction they show deficits in accessing contextual knowledge that further specifies a general concept or helps to identify an object or a person. METHODOLOGY/PRINCIPAL FINDINGS: Using functional magnetic resonance imaging, we investigated the neural networks associated with the perception of personal familiar faces and places in patients with amnestic mild cognitive impairment and healthy control subjects. Irrespective of stimulus type, patients compared to control subjects showed lower activity in right prefrontal brain regions when perceiving personally familiar versus unfamiliar faces and places. Both groups did not show different neural activity when perceiving faces or places irrespective of familiarity. CONCLUSIONS/SIGNIFICANCE: Our data highlight changes in a frontal cortical network associated with knowledge-based personal familiarity among patients with amnestic mild cognitive impairment. These changes could contribute to deficits in social cognition and may reduce the patients' ability to transition from basic to complex situations and tasks

Age-dependent differences in the neural mechanisms supporting long-term

Autobiographical memories enable us to mentally reconstruct and relive past events, which is essential for one's personal identity. Unfortunately, this complex memory system is susceptible to age-related deterioration, possibly changing the way episodic information is being processed in older adults. The aim of this study was to investigate whether age influences the neural activity associated with content (episodic versus semantic) and remoteness (recent versus remote) of memories. Using functional magnetic resonance imaging in healthy older and young adults, we found significant age-dependent differences in the neural networks underlying memory content but not remoteness. Our data suggest an age-associated functional reorganization in the neural networks underlying long-term declarative memory. Relative increase in activity of posterior brain regions could reflect changes in visuospatial processing during episodic memory retrieval in older adults

Altered neural network supporting declarative long-term memory in mild cognitive impairment

Autobiographical episodic memory represents a subsystem of declarative long-term memory and largely depends on combining information from multiple sources. The purpose of this study was to assess neural correlates of declarative long-term memory in patients with amnestic mild cognitive impairment (MCI) and controls using fMRI and a task requiring autobiographical and semantic memory retrieval. Comparison of the network supporting episodic autobiographical and semantic memory irrespective of remoteness (recent and remote) revealed significant activations in right parietal cortex and precuneus bilaterally in the patients. Autobiographical episodic versus semantic memory retrieval in the controls led to significant bilateral activations of the parietal-temporal junction, left temporal pole, anterior cingulate, retrosplenial cortex and cerebellum. In contrast, MCI patients activated left supplementary motor area, left premotor and superior temporal cortex. In MCI patients compared to controls a dysfunction of the retrosplenial cortex during memory retrieval was revealed by a lack of differential activation in relation to recency of memories and memory type. Our data suggest that MCI leads to a loss of specificity in the neural network supporting declarative long-term memory

Neuroimaging Findings in Mild Cognitive Impairment

The clinical construct of mild cognitive impairment (MCI) identifies a syndrome of cognitive deficit which is not significant enough to interfere with daily activities, whose fate is unpredictable without establishing the underlying cause. Thus, MCI, though being the natural \u201creservoir\u201d of subsequent dementing neurodegenerative diseases, can be provoked by a variety of psychiatric and systemic diseases as well as by drugs, alcohol, and substance abuse. In this context, morphological and, especially, functional neuroimaging by means of multitracer SPECT and PET are useful tools to provide clue information on the underlying pathological process. Both MRI and SPECT/PET have been included as indicative or supportive biomarkers in the diagnostic criteria of a variety of neurodegenerative conditions, already at the MCI stage, ranging from Alzheimer\u2019s disease to dementia with Lewy bodies and to frontotemporal dementia. New developments include MRI high-field equipment and functional techniques, fluorinated PET radiopharmaceuticals for protein Tau detection, and receptor studies. In the advanced memory clinics, appropriate use of neuroimaging is nowadays paramount for the correct diagnosis of cognitive disorders