Prefrontal serotonin depletion impairs egocentric, but not allocentric working memory in rats

Brain Dynamics of Spatial Reference Frame Proclivity in Active Navigation

Recent research into navigation strategy of different spatial reference frames (self-centered egocentric reference frame and environment-centered allocentric reference frame) has revealed that the parietal cortex plays an important role in processing allocentric information to provide a translation function between egocentric and allocentric spatial reference frames. However, most studies merely focused on a passive experimental environment, which is not truly representative of our daily spatial learning/navigation tasks. This study investigated the factor associated with brain dynamics that causes people to switch their preferred spatial strategy in both active and passive navigations to bridge the gap. Virtual reality (VR) technique and Omni treadmill are applied to realize actively walking for active navigation, and for passive navigation, participants were sitting while conducting the same task. Electroencephalography (EEG) signals were recorded to monitor spectral perturbations on transitions between egocentric and allocentric frames during a path integration task. Forty-one right-handed male participants from authors' university participated this study. Our brain dynamics results showed navigation involved areas including the parietal cortex with modulation in the alpha band, the occipital cortex with beta and low gamma band perturbations, and the frontal cortex with theta perturbation. Differences were found between two different turning-angle paths in the alpha band in parietal cluster event-related spectral perturbations (ERSPs). In small turning-angle paths, allocentric participants showed stronger alpha desynchronization than egocentric participants; in large turning-angle paths, participants for two reference frames had a smaller difference in the alpha frequency band. Behavior results of homing errors also corresponded to brain dynamic results, indicating that a larger angle path caused the allocentric to have a higher tendency to become egocentric navigators in the active navigation environment.

Neurobiology of Anorexia Nervosa: Serotonin Dysfunctions Link Self-Starvation with Body Image Disturbances through an Impaired Body Memory

The etiology of anorexia nervosa (AN) is still unclear, despite that it is a critical and potentially mortal illness. A recent neurobiological model considers AN as the outcome of dysfunctions in the neuronal processes related to appetite and emotionality (Kaye et al., 2009, 2013). However, this model still is not able to answer a critical question: What is behind body image disturbances (BIDs) in AN? The article starts its analysis from reviewing some of the studies exploring the effects of the serotonin systems in memory (episodic, working, and spatial) and its dysfunctions. The review suggests that serotonin disturbances may: (a) facilitate the encoding of third person (allocentric) episodic memories; (b) facilitate the consolidation of emotional episodic memories (e.g., teasing), if preceded by repeated stress; (c) reduce voluntary inhibition of mnestic contents; (d) impair allocentric spatial memory. If we discuss these results within the interpretative frame suggested by the “Allocentric Lock Hypothesis” (Riva, 2012, 2014), we can hypothesize that altered serotoninergic activity in AN patients: (i) improves their ability to store and consolidate negative autobiographical memories, including those of their body, in allocentric perspective; (ii) impairs their ability to trigger voluntary inhibition of the previously stored negative memory of the body; (iii) impairs their capacity to retrieve/update allocentric information. Taken together, these points suggest a possible link between serotonin dysfunctions, memory impairments and BIDs: the impossibility of updating a disturbed body memory using real time experiential data—I'm locked to a wrong body stored in long term memory—pushes AN patients to control body weight and shape even when underweight.

6-Hydroxydopamine-Induced Dopamine Reductions in the Nucleus Accumbens, but not the Medial Prefrontal Cortex, Impair Cincinnati Water Maze Egocentric and Morris Water Maze Allocentric Navigation in Male Sprague-Dawley Rats

The nucleus accumbens (Nacc) and medial prefrontal cortex (mPFC) receive dopaminergic innervation from the ventral tegmental area and are involved in learning. Male rats with 6-hydroxydopamine (6-OHDA)-induced dopaminergic and noradrenergic reductions in the Nacc or mPFC were tested for allocentric and egocentric learning to determine their role in these forms of neuroplasticity. mPFC dopaminergic and noradrenergic reductions did not result in changes to either type of learning or memory. Nacc dopaminergic and noradrenergic reductions resulted in allocentric learning and memory deficits in the Morris water maze (MWM) on acquisition, reversal, and probe trials. MWM cued performance was also affected, but straight-channel swim times and swim speed during hidden platform trials in the MWM were not affected. Nacc dopaminergic and noradrenergic reductions also impaired egocentric learning in the Cincinnati water maze (CWM). Nacc-lesioned animals tested in the CWM in an alternate path through the maze were not significantly affected. 6-OHDA injections in the Nacc resulted in 63 % dopamine and 62 % norepinephrine reductions in the Nacc and 23 % reductions in adjacent dorsal striatum. 6-OHDA injections in the mPFC resulted in 88 % reductions in dopamine and 59 % reductions in norepinephrine. Hence, Nacc dopamine and/or norepinephrine play a role in egocentric and allocentric learning and memory, while mPFC dopamine and norepinephrine do not.

EEG correlates of spatial orientation in the human retrosplenial complex

Studies on spatial navigation reliably demonstrate that the retrosplenial complex (RSC) plays a pivotal role for allocentric spatial information processing by transforming egocentric and allocentric spatial information into the respective other spatial reference frame (SRF). While more and more imaging studies investigate the role of the RSC in spatial tasks, high temporal resolution measures such as electroencephalography (EEG) are missing. To investigate the function of the RSC in spatial navigation with high temporal resolution we used EEG to analyze spectral perturbations during navigation based on allocentric and egocentric SRF. Participants performed a path integration task in a clearly structured virtual environment providing allothetic information. Continuous EEG recordings were decomposed by independent component analysis (ICA) with subsequent source reconstruction of independent time source series using equivalent dipole modeling. Time-frequency transformation was used to investigate reference frame-specific orientation processes during navigation as compared to a control condition with identical visual input but no orientation task. Our results demonstrate that navigation based on an egocentric reference frame recruited a network including the parietal, motor, and occipital cortices with dominant perturbations in the alpha band and theta modulation in frontal cortex. Allocentric navigation was accompanied by performance-related desynchronization of the 8-13 Hz frequency band and synchronization in the 12-14 Hz band in the RSC. The results support the claim that the retrosplenial complex is central to translating egocentric spatial information into allocentric reference frames. Modulations in different frequencies with different time courses in the RSC further provide first evidence of two distinct neural processes reflecting translation of spatial information based on distinct reference frames and the computation of heading changes.

Long-term administration of Greek Royal Jelly improves spatial memory and influences the concentration of brain neurotransmitters in naturally aged Wistar male rats

ETHNOPHARMACOLOGICAL RELEVANCE

Royal Jelly (RJ) is a bee-derived product that has been traditionally used in the European and Asian systems of medicine for longevity. RJ has various pharmacological activities that may prevent aging e.g., anti-inflammatory, anti-oxidative, anti-hypercholesterolemic and anti-hyperglycemic properties.

AIM OF THE STUDY

To evaluate the behavioral and neurochemical effects of long-term oral, previously chemically analyzed, Greek RJ administration to aged rats.

MATERIALS AND METHODS

RJ powder was given to 18-month old male Wistar rats (50 and 100mg of powder/kg b.w./day) by gastric gavage for 2 months. The spatial memory was assessed in the water maze and next the level of neurotransmitters, their metabolites and utilization in the selected brain regions were estimated.

RESULTS

The improvement of memory in rats pretreated with the smaller dose of RJ was observed compared with controls. In biochemical examination mainly the depletion of dopamine and serotonin in the prefrontal cortex along with an increase in their metabolite concentration and turnover were seen.

CONCLUSION

Better cognitive performance in the old animals using a non-toxic, natural food product in the view of the process of the aging of human population is noteworthy. Our results contribute towards validation of the traditional use of RJ in promoting a better quality of life in old age.

Influences of COMT and 5-HTTLPR polymorphisms on cognitive flexibility in healthy women: inhibition of prepotent responses and memory updating

Understanding genetic factors that affect monoamine neurotransmitters flux in prefrontal cortex may help to further specify the complex neurobiological processes that underlie cognitive function and dysfunction in health and illness. The current study examined the associations between the polymorphisms of dopaminergic (COMT Met158Val) and serotoninergic (5-HTTLPR) genes and the sequential pattern of responses in a motor random generation task providing well-established indexes for executive functioning in a large sample of 255 healthy women. Participants homozygous for the Met allele of the COMT polymorphism showed impaired inhibition of prepotent responses, whereas individuals homozygous for the s-allele of the 5-HTTLPR showed a restricted ability to update information in working memory. Taken together the results indicate differentiated influences of dopaminergic and serotonergic genes on important and definite executive sub-processes related to cognitive flexibility.