Functional imaging during recognition of personally familiar faces and places in Alzheimer's disease.

Alzheimer's disease (AD) patients show better everyday functioning in a familiar setting, but they have a reduced ability to access contextual details and episodes associated with a familiar person or environment. This suggests a dysfunction in the neural networks associated with stimulus identification. Using functional magnetic resonance imaging, we investigated the neural activity during the recognition of personally familiar and unfamiliar faces and places among AD patients and elderly controls. We did not find a group difference in the neural activity within brain areas important for perceptual familiarity recognition. Patients showed reduced activation for familiar stimuli in prefrontal brain areas known to be important for retrieving contextual information for a stimulus when compared with controls. These changes may contribute to how AD patients experience a personally familiar face or place.

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 declarative memories.

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.

Age and the neural network of personal familiarity.

BACKGROUND: Accessing information that defines personally familiar context in real-world situations is essential for the social interactions and the independent functioning of an individual. Personal familiarity is associated with the availability of semantic and episodic information as well as the emotional meaningfulness surrounding a stimulus. These features are known to be associated with neural activity in distinct brain regions across different stimulus conditions (e.g., when perceiving faces, voices, places, objects), which may reflect a shared neural basis. Although perceiving context-rich personal familiarity may appear unchanged in aging on the behavioral level, it has not yet been studied whether this can be supported by neuroimaging data. METHODOLOGY/PRINCIPAL FINDINGS: We used functional magnetic resonance imaging to investigate the neural network associated with personal familiarity during the perception of personally familiar faces and places. Twelve young and twelve elderly cognitively healthy subjects participated in the study. Both age groups showed a similar activation pattern underlying personal familiarity, predominantly in anterior cingulate and posterior cingulate cortices, irrespective of the stimulus type. The young subjects, but not the elderly subjects demonstrated an additional anterior cingulate deactivation when perceiving unfamiliar stimuli. CONCLUSIONS/SIGNIFICANCE: Although we found evidence for an age-dependent reduction in frontal cortical deactivation, our data show that there is a stimulus-independent neural network associated with personal familiarity of faces and places, which is less susceptible to aging-related changes.

Overgenerality of autobiographical memory in people with amnestic mild cognitive impairment and early Alzheimer's disease.

Episodic autobiographical memory (ABM) is important for social functioning. Loss of specificity in ABM retrieval has been observed in people with mild to moderate Alzheimer's disease (AD). Our aim was to extend these findings to subjects with amnestic mild cognitive impairment (aMCI) and very early AD. We performed a cued ABM task with both subject groups and healthy elderly controls. Although aMCI participants performed better than early AD subjects both showed reduced specificity of ABM retrieval when compared with controls. We conclude that qualitative memory retrieval deficits could contribute to social functioning impairment in people with aMCI and early AD, and highlight the complexity of symptoms already present in early stages of cognitive impairment.

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.