A medial temporal lobe division of labor: insights from memory in aging and early Alzheimer disease.

Dual process theories of recognition memory posit that recollection and familiarity represent dissociable processes. Animal studies and human functional imaging experiments support an anatomic dissociation of these processes in the medial temporal lobes (MTL). By this hypothesis, recollection may be dependent on the hippocampus, while familiarity appears to rely on extrahippocampal MTL (ehMTL) structures, particularly perirhinal and lateral entorhinal cortices. Despite these findings, the dual process model and these anatomic mappings remain controversial, in part because the study of patients with lesions to the MTL has been limited and has revealed predominantly single dissociations. We examined measures of recollection and familiarity in three groups (normal older adults, amnesic-mild cognitive impairment, Alzheimer's disease) in which these memory measures and the relative integrity of MTL structures are variable, thus enhancing our power to detect MTL-memory relationships. Recollection and familiarity and volumes of hippocampus and ehMTL, defined as a region including entorhinal/perirhinal cortices and parahippocampus, were measured. Regression analyses revealed a stronger relationship of recollection with the hippocampus compared to ehMTL, while familiarity was more highly related to ehMTL compared to hippocampus. These results are consistent with a division of labor in the MTL and the dual process model.

Postconcussive symptoms are associated with compensatory cortical recruitment during a working memory task.

BACKGROUND: The severity of sports-related concussion is often characterized by the number and severity of postconcussive symptoms (eg, headache, dizziness, difficulty concentrating). Although the level of postconcussive symptoms after injury is believed to index the severity of the neurological insult sustained, studies examining the relationship between symptom severity and neural functioning in concussed athletes remain rare. OBJECTIVE: This exploratory study examined the association between self-reported symptom severity and functional activation on a working memory task in a group of 16 recently concussed student athletes. METHODS: Functional magnetic resonance imaging was used to examine the relationship of symptom severity to brain activation during a working memory task in 16 concussed subjects. RESULTS: Findings indicated that symptom severity was associated with regionally specific hyperactivation during a working memory task, even though symptom severity was not significantly related to task accuracy. CONCLUSION: The results add to a growing body of literature that demonstrates that functional neuroimaging may have the potential to serve as a sensitive biomarker of the severity of concussion and mild traumatic brain injury.

Brain activation, response inhibition, and increased risk for substance use disorder.

BACKGROUND: Youth at high risk for developing substance use disorders (SUDs) often exhibit differences which suggest inhibitory impairments when compared to average risk youth. METHODS: To examine the underlying neural activity related to these impairments, functional MRI (fMRI) was employed in adolescents during an antisaccade task requiring inhibition of an eye movement response. Each subject's level of neurobehavioral disinhibition (ND) was assessed using a multi-informant, multi-method approach, which has been shown to be highly predictive of SUD onset. The fMRI data was categorized into neural regions of interest according to total frontal, parietal, occipital, and temporal lobe activation. RESULTS: Results demonstrated that ND score was negatively correlated with total amount of frontal activation, but was not significantly correlated with total activation in any other neural region. CONCLUSIONS: These results indicate deficits in frontal activation in youth with high amounts of ND, suggesting a possible developmental delay of executive processes in high-risk youth.