Gender differences in navigation performance are associated with differential theta and high-gamma activities in the hippocampus and parahippocampus

Less spatial exploration is associated with poorer spatial memory in midlife adults

Introduction

Despite its importance for navigation, very little is known about how the normal aging process affects spatial exploration behavior. We aimed to investigate: (1) how spatial exploration behavior may be altered early in the aging process, (2) the relationship between exploration behavior and subsequent spatial memory, and (3) whether exploration behavior can classify participants according to age.

Methods

Fifty healthy young (aged 18-28) and 87 healthy midlife adults (aged 43-61) freely explored a desktop virtual maze, learning the locations of nine target objects. Various exploration behaviors (object visits, distance traveled, turns made, etc.) were measured. In the test phase, participants navigated from one target object to another without feedback, and their wayfinding success (% correct trials) was measured.

Results

In the exploration phase, midlife adults exhibited less exploration overall compared to young adults, and prioritized learning target object locations over maze layout. In the test phase, midlife adults exhibited less wayfinding success when compared to the young adults. Furthermore, following principal components analysis (PCA), regression analyses indicated that both exploration quantity and quality components were associated with wayfinding success in the midlife group, but not the young adults. Finally, we could classify participants according to age with similar accuracy using either their exploration behavior or wayfinding success scores.

Discussion

Our results aid in the understanding of how aging impacts spatial exploration, and encourages future investigations into how pathological aging may affect spatial exploration behavior.

Effective connectivity of working memory performance: a DCM study of MEG data

Visual working memory (WM) engages several nodes of a large-scale network that includes frontal, parietal, and visual regions; however, little is understood about how these regions interact to support WM behavior. In particular, it is unclear whether network dynamics during WM maintenance primarily represent feedforward or feedback connections. This question has important implications for current debates about the relative roles of frontoparietal and visual regions in WM maintenance. In the current study, we investigated the network activity supporting WM using MEG data acquired while healthy subjects performed a multi-item delayed estimation WM task. We used computational modeling of behavior to discriminate correct responses (high accuracy trials) from two different types of incorrect responses (low accuracy and swap trials), and dynamic causal modeling of MEG data to measure effective connectivity. We observed behaviorally dependent changes in effective connectivity in a brain network comprising frontoparietal and early visual areas. In comparison with high accuracy trials, frontoparietal and frontooccipital networks showed disrupted signals depending on type of behavioral error. Low accuracy trials showed disrupted feedback signals during early portions of WM maintenance and disrupted feedforward signals during later portions of maintenance delay, while swap errors showed disrupted feedback signals during the whole delay period. These results support a distributed model of WM that emphasizes the role of visual regions in WM storage and where changes in large scale network configurations can have important consequences for memory-guided behavior.

Theta oscillatory power decreases in humans are associated with spatial learning in a virtual water maze task

Theta oscillations (4-8 Hz) in humans play a role in navigation processes, including spatial encoding, retrieval and sensorimotor integration. Increased theta power at frontal and parietal midline regions is known to contribute to successful navigation. However, the dynamics of cortical theta and its role in spatial learning are not fully understood. This study aimed to investigate theta oscillations via electroencephalogram (EEG) during spatial learning in a virtual water maze. Participants were separated into a learning group (n = 25) who learned the location of a hidden goal across 12 trials, or a time-matched non-learning group (n = 25) who were required to simply navigate the same arena, but without a goal. We compared all trials, at two phases of learning, the trial start and the goal approach. We also compared the first six trials with the last six trials within-groups. The learning group showed reduced low-frequency theta power at the frontal and parietal midline during the start phase and largely reduced theta combined with a short increase at both midlines during the goal-approach phase. These patterns were not found in the non-learning group, who instead displayed extensive increases in low-frequency oscillations at both regions during the trial start and at the parietal midline during goal approach. Our results support the theory that theta plays a crucial role in spatial encoding during exploration, as opposed to sensorimotor integration. We suggest our findings provide evidence for a link between learning and a reduction of theta oscillations in humans.

Motivation moderates gender differences in navigation performance

Gender differences in navigation performance are a recurrent and controversial topic. Previous research suggests that men outperform women in navigation tasks and that men and women exhibit different navigation strategies. Here, we investigate whether motivation to complete the task moderates the relationship between navigation performance and gender. Participants learned the locations of landmarks in a novel virtual city. During learning, participants could trigger a top-down map that depicted their current position and the locations of the landmarks. During testing, participants were divided into control and treatment groups and were not allowed to consult the map. All participants were given 16 minutes to navigate to the landmarks, but those in the treatment group were monetarily penalized for every second they spent completing the task. Results revealed a negative relationship between physiological arousal and the time required to locate the landmarks. In addition, gender differences in strategy were found during learning, with women spending more time with the map and taking 40% longer than men to locate the landmarks. Interestingly, an interaction between gender and treatment group revealed that women in the control group required more time than men and women in the treatment group to retrieve the landmarks. During testing, women in the control group also took more circuitous routes compared to men in the control group and women in the treatment group. These results suggest that a concurrent and relevant stressor can motivate women to perform similarly to men, helping to diminish pervasive gender differences found in the navigation literature.

Theta and gamma oscillatory dynamics in mouse models of Alzheimer's disease: A path to prospective therapeutic intervention

Understanding the neural basis of cognitive deficits, a key feature of Alzheimer's disease (AD), is imperative for achieving the therapy of the disease. Rhythmic oscillatory activities in neural systems are a fundamental mechanism for diverse brain functions, including cognition. In several neurological conditions like AD, aberrant neural oscillations have been shown to play a central role. Furthermore, manipulation of brain oscillations in animals has confirmed their impact on cognition and disease. In this article, we review the evidence from mouse models that shows how synchronized oscillatory activity is intricately linked to AD machinery. We primarily focus on recent reports showing abnormal oscillatory activities at theta and gamma frequencies in AD condition and their influence on cellular disturbances and cognitive impairments. A thorough comprehension of the role that neuronal oscillations play in AD pathology should pave the way to therapeutic interventions that can curb the disease.

The medial entorhinal cortex mediates basolateral amygdala effects on spatial memory and downstream activity-regulated cytoskeletal-associated protein expression

The basolateral amygdala (BLA) modulates the consolidation of dorsal hippocampus (DH)-dependent spatial and dorsolateral striatum (DLS)-dependent cued-response memories, often in competition with one another. Evidence suggests that a critical mechanism for BLA influences on memory consolidation is via effects on activity-regulated cytoskeletal-associated protein (ARC) in downstream brain regions. However, the circuitry by which the BLA modulates ARC in multiple competing memory systems remains unclear. Prior evidence indicates that optogenetic stimulation of BLA projections to the medial entorhinal cortex (mEC) enhances the consolidation of spatial learning and impairs the consolidation of cued-response learning, suggesting this pathway provides a circuit for favoring one system over another. Therefore, we hypothesized the BLA-mEC pathway mediates effects on downstream ARC-based synaptic plasticity related to these competing memory systems. To address this, male and female Sprague-Dawley rats underwent spatial or cued-response Barnes maze training and, 45 min later, were sacrificed for ARC analysis in synaptoneurosomes from the DH and DLS. Initial experiments found that spatial training alone increased ARC levels in the DH above those observed in control rats and rats that underwent a cued-response version of the task. Postspatial training optogenetic stimulation of the BLA-mEC pathway altered the balance of ARC expression in the DH vs. DLS, specifically shifting the balance in favor of the DH-based spatial memory system, although the precise region of ARC changes differed by sex. These findings suggest that BLA-mEC pathway influences on ARC in downstream regions are a mechanism by which the BLA can favor one memory system over another.

Pregnancy swimming prevents early brain mitochondrial dysfunction and causes sex-related long-term neuroprotection following neonatal hypoxia-ischemia in rats

Neonatal hypoxia-ischemia (HI) is a major cause of cognitive impairments in infants. Antenatal strategies improving the intrauterine environment can have high impact decreasing pregnancy-derived intercurrences. Physical exercise alters the mother-fetus unity and has been shown to prevent the energetic challenge imposed by HI. This study aimed to reveal neuroprotective mechanisms afforded by pregnancy swimming on early metabolic failure and late cognitive damage, considering animals' sex as a variable. Pregnant Wistar rats were submitted to daily swimming exercise (20' in a tank filled with 32 °C water) during pregnancy. Neonatal HI was performed in male and female pups at postnatal day 7. Electron chain transport, mitochondrial mass and function and ROS formation were assessed in the right brain hemisphere 24 h after HI. From PND45, reference and working spatial memory were tested in the Morris water maze. MicroPET-FDG images were acquired 24 h after injury (PND8) and at PND60, following behavioral analysis. HI induced early energetic failure, decreased enzymatic activity in electron transport chain, increased production of ROS in cortex and hippocampus as well as caused brain glucose metabolism dysfunction and late cognitive impairments. Maternal swimming was able to prevent mitochondrial dysfunction and to improve spatial memory. The intergenerational effects of swimming were sex-specific, since male rats were benefited most. In conclusion, maternal swimming was able to affect the mitochondrial response to HI in the offspring's brains, preserving its function and preventing cognitive damage in a sex-dependent manner, adding relevant information on maternal exercise neuroprotection and highlighting the importance of mitochondria as a therapeutic target for HI neuropathology.