An fMRI study on memory discriminability for complex visual scenes

Hippocampal Estrogen Signaling Mediates Sex Differences in Retroactive Interference

Despite being a crucial physiological function of the brain, the mechanisms underlying forgetting are still poorly understood. Estrogens play a critical role in different brain functions, including memory. However, the effects of sex hormones on forgetting vulnerabilitymediated by retroactive interference (RI), a phenomenon in which newly acquired information interferes with the retrieval of already stored information, are still poorly understood. The aim of our study was to characterize the sex differences in interference-mediated forgetting and identify the underlying molecular mechanisms. We found that adult male C57bl/6 mice showed a higher susceptibility to RI-dependent memory loss than females. The preference index (PI) in the NOR paradigm was 52.7 ± 5.9% in males and 62.3 ± 13.0% in females. The resistance to RI in female mice was mediated by estrogen signaling involving estrogen receptor α activation in the dorsal hippocampus. Accordingly, following RI, females showed higher phosphorylation levels (+30%) of extracellular signal-regulated kinase1/2 (ERK1/2) in the hippocampus. Pharmacological inhibition of ERK1/2 made female mice prone to RI. The PI was 70.6 ± 11.0% in vehicle-injected mice and 47.4 ± 10.8% following PD98059 administration. Collectively, our data suggest that hippocampal estrogen α receptor-ERK1/2 signaling is critically involved in a pattern separation mechanism that inhibits object-related RI in female mice.

Neural processing of criticism and positive comments from relatives in individuals with schizotypal personality traits

OBJECTIVES. High negative expressed emotion by family members towards schizophrenia patients increases the risk of subsequent relapse. The study aimed to determine whether individuals with high schizotypy (HS) and low schizotypy (LS) would differ in activation of brain areas involved in cognitive control when listening to relative criticism. METHODS. Twelve HS and 12 LS individuals listened to relative's critical, positive and neutral comments about them while undergoing functional MRI. Activation maps in the two groups during the comments were compared using SPM5. RESULTS. The left superior frontal and middle frontal gyri and bilateral posterior cingulate cortex were activated during criticism, compared to neutral comments, across all participants. While there were no group differences in brain activity for criticism versus neutral comments, the HS group, who had lower current mood relative to the LS group, activated to a lesser extent the thalamus, insula, putamen and brain stem during positive, compared to neutral, comments. CONCLUSIONS. Listening to relative criticism in healthy individuals engages brain areas for cognitive control of negative emotion and self-referential processing. However, HS individuals may have an attenuated ability to respond to rewarding aspects of positive comments due to their lower current mood.

Neural structures and mechanisms involved in scene recognition: a review and interpretation

Since the discovery in 1996 that a region within caudal parahippocampal cortex subserves learning and recall of topographical information, numerous studies aimed at elucidating the structures and pathways involved in scene recognition have been published. Neuroimaging studies, in particular, have revealed the locations and identities of some of the principal cortical structures that mediate these faculties. In the present study the detailed organization of the system is examined, based on a meta-analysis of neuroimaging studies of scene processing in human subjects, combined with reviews of the results of lesions on this type of processing, single neuron studies, and available hodological data in non-human primates. A cortical hierarchy of structures that mediate scene recognition is established based on these data, and an attempt is made to determine the function of the individual components of the system.

Comparison of associative learning-related signals in the macaque perirhinal cortex and hippocampus

Strong evidence suggests that the macaque monkey perirhinal cortex is involved in both the initial formation as well as the long-term storage of associative memory. To examine the neurophysiological basis of associative memory formation in this area, we recorded neural activity in this region as monkeys learned new conditional-motor associations. We report that a population of perirhinal neurons signal newly learned associations by changing their firing rate correlated with the animal's behavioral learning curve. Individual perirhinal neurons signal learning of one or more associations concurrently and these neural changes could occur before, at the same time, or after behavioral learning was expressed. We also compared the associative learning signals in the perirhinal cortex to our previous findings in the hippocampus. We report global similarities in both the learning-related and task-related activity seen across these areas as well as clear differences in the within and across trial timing and relative proportion of different subtypes of learning-related signals. Taken together, these findings emphasize the important role of the perirhinal cortex in new associative learning and suggest that the perirhinal cortex together with the hippocampus contribute importantly to conditional-motor associative memory formation.