Rao, A. M. | Search bioRxiv

bioRxiv2024

Social isolation reduces metabolic rate and social preference in Wild-type Zebrafish (Danio rerio)

Group living is a common feature of many animals and serves a variety of functions, including predator avoidance, collective foraging, and reproduction. Individuals from group-living species may face isolation from their social group in their natural environment. Prior research has shown that social isolation in zebrafish (Danio rerio), a highly social fish, results in physiological and behavioural changes, including reduced locomotor activity and loss of interest in their environment. We investigated whether social isolation was associated with differences in dissolved oxygen consumption rate, movement speed, and social preference in adult zebrafish. We subjected fish to one month of visual and olfactory social isolation, and measured metabolic rate via dissolved oxygen consumption rate before and after social isolation. A control group was not subjected to any form of social isolation but held in comparable housing. We measured movement speed and social interaction before and after social isolation using a social preference assay. We found that socially isolated fish show a significant decrease in oxygen consumption rate compared to Day 0 isolation baseline levels, whereas control fish did not show this decrease. After a month of social isolation fish also showed lower social preference, and lower movement speed. These findings could suggest reduced energy expenditure in the context of social isolation in this species. This work enhances our understanding of the physiological and behavioural consequences of isolation in social animals.

ecology↗

bioRxiv2024

Synchronous theta networks characterize successful memory retrieval

Memory retrieval activates regions across the brain, including not only the hippocampus and medial temporal lobe (MTL), but also frontal, parietal, and lateral temporal cortical regions. What remains unclear, however, is how these regions communicate to organize retrieval-specific process-ing. Here, we elucidate the role of theta (3-8 Hz) synchronization, broadly implicated in memory function, during the spontaneous retrieval of episodic memories. Analyzing a dataset of 382 neurosurgical patients (213 male, 168 female, 1 unknown) implanted with intracranial electrodes who completed a free recall task, we find that synchronous networks of theta phase synchrony span the brain in the moments before spontaneous recall, in comparison to periods of deliberation and incorrect recalls. Hubs of the retrieval network, which systematically synchronize with other regions, appear throughout the prefrontal cortex and lateral and medial temporal lobes, as well as other areas. Theta synchrony increases appear more prominently for slow (3 Hz) theta than for fast (8 Hz) theta in the recall-deliberation contrast, but not in the encoding or recall-intrusion contrast, and theta power and synchrony positively correlate throughout the theta band. These results implicate diffuse brain-wide synchronization of theta rhythms, especially slow theta, in episodic memory retrieval. Significance StatementAnalyzing intracranial recordings from 382 subjects who completed an episodic free recall experi-ment, we study the brain-wide theta synchrony effects of memory retrieval. The literature has not previously described the whole-brain regional distribution of these effects nor studied them with respect to intrusions. We show that a whole-brain theta synchrony effect marks the recall accuracy contrast, that distributed synchronous hubs constitute a whole-brain retrieval network, and that theta synchrony in the successful encoding, successful retrieval, and recall accuracy contrasts corre-lates positively with theta power increases at a region. These findings advance our understanding of the role and localization of theta synchrony effects during human memory retrieval.

neuroscience↗