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Memory for events from the distant past relies on multiple brain regions, but little is known about the underlying neural dynamics that give rise to such abilities. We recorded neural activity in the hippocampus and retrosplenial cortex of two female rhesus macaques as they visually selected targets in year-old and newly acquired object-scene associations. Whereas hippocampal activity was unchanging with memory age, the retrosplenial cortex responded with greater magnitude alpha oscillations (10–15 Hz) and greater phase locking to memory-guided eye movements during retrieval of old events. A similar old-memory enhancement was observed in the anterior cingulate cortex but in a beta2/gamma band (28–35 Hz). In contrast, remote retrieval was associated with decreased gamma-band synchrony between the hippocampus and each neocortical area. The increasing retrosplenial alpha oscillation and decreasing hippocampocortical synchrony with memory age may signify a shift in frank memory allocation or, alternatively, changes in selection among distributed memory representations in the primate brain.SIGNIFICANCE STATEMENTMemory depends on multiple brain regions, whose involvement is thought to change with time. Here, we recorded neuronal population activity from the hippocampus and retrosplenial cortex as nonhuman primates searched for objects embedded in scenes. These memoranda were either newly presented or a year old. Remembering old material drove stronger oscillations in the retrosplenial cortex and led to a greater locking of neural activity to search movements. Remembering new material revealed stronger oscillatory synchrony between the hippocampus and retrosplenial cortex. These results suggest that with age, memories may come to rely more exclusively on neocortical oscillations for retrieval and search guidance and less on long-range coupling with the hippocampus.

Background The pedunculopontine tegmental (PPT) nucleus is a heterogeneous nucleus with several functions including cardiovascular regulation. The presence of GABAA receptor has been shown in the PPT. Therefore, the cardiovascular effects of this receptor were examined. Methods Rats were divided into: Control; Muscimol; Bicuculline (BMI); Hexamethonium (Hexa) + BMI and Atropine + BMI groups. The femoral vein and artery were cannulated for drug administration and recording of cardiovascular parameters, respectively. Muscimol (a GABAA agonist; 1.5 and 2.5 nmol), BMI (a GABAA antagonist; 0.1 and 0.2 nmol) were stereotaxically microinjected into the PPT. To evaluate the peripheral cardiovascular mechanisms of GABAA receptors, Hexa (a ganglionic blocker; 10 mg/kg) and atropine (a muscarinic receptor antagonist; 1 mg/kg) were intravenously (iv) injected before BMI (0.2 nmol). The average changes of mean arterial pressure (ΔMAP), systolic blood pressure (ΔSBP) and heart rate (ΔHR) in different intervals were calculated and compared both within and between case group and control group (repeated measures ANOVA). The peak changes in each group were also calculated and compared with those of the control group (independent sample t-test). Results Both doses of BMI significantly increased ΔMAP, ΔSBP and ΔHR compared to control, while the only higher dose of muscimol significantly decreased ΔSBP. Iv injection of Hexa significantly attenuated ΔMAP, ΔSBP and ΔHR responses induced by BMI but atropine did not affect. Conclusions Our results demonstrate that GABAA receptor of the PPT has a tonic inhibitory effect on the cardiovascular system and its peripheral effect mostly is mediated by sympathetic system.

The pedunculopontine tegmental (PPT) nucleus is a heterogeneous nucleus with several functions including cardiovascular regulation. The presence of GABARats were divided into: Control; Muscimol; Bicuculline (BMI); Hexamethonium (Hexa)+BMI and Atropine+BMI groups. The femoral vein and artery were cannulated for drug administration and recording of cardiovascular parameters, respectively. Muscimol (a GABABoth doses of BMI significantly increased ΔMAP, ΔSBP and ΔHR compared to control, while the only higher dose of muscimol significantly decreased ΔSBP. Iv injection of Hexa significantly attenuated ΔMAP, ΔSBP and ΔHR responses induced by BMI but atropine did not affect.Our results demonstrate that GABA