Biology subjects

Ness, H.

Publications and source records attributed to Ness, H..

4 recordsLinked to original sources

bioRxiv2026

Rats use darting as a strategy to navigate between reward and safety during platform-mediated active avoidance under different social contexts.

The platform-mediated active avoidance (PMA) task has been used as a rodent model of decision-based active avoidance in which rat learn to avoid a tone-signaled shock. Prior studies utilizing the PMA task have primarily investigated avoidance, freezing, and food-seeking behaviors, but few studies have thoroughly assessed darting behavior, a more recently identified measure of fear that has been largely explored in conditional fear paradigms. Here, we investigated the properties of darting that occur during the PMA task, in which rats either acquired the PMA task alone or with a social partner. We found that rats undergoing solitary PMA produced significantly more darting bouts, whereas rats undergoing social partner PMA produced darts that were faster and shorter in duration. We also found that darting in solitary PMA was predominantly concentrated at the platform, whereas darting in social partner PMA occurred more often outside of the platform and lever zones. Analysis of darting trajectories, which included movements surrounding each darting bout, revealed that darting was embedded in a broader movement strategy between the platform and lever zones, especially during solitary PMA, and this pattern increased across training days. These findings suggest that darting during the PMA task serves as a learned strategy to navigate between reward and safety and is modulated by social context, which is distinct from escape-like darting observed in auditory fear conditioning.

animal behavior and cognition↗

bioRxiv2022

Sustained upregulation of widespread hippocampal-neocortical coupling following memory encoding

Systems consolidation of new experiences into lasting episodic memories involves interactions between hippocampus and the neocortex. Evidence of this process is seen already during early awake post-encoding rest periods. Functional MRI (fMRI) studies have demonstrated increased hippocampal coupling with task-relevant perceptual regions and reactivation of stimulus-specific encoding patterns following intensive encoding tasks. Here we investigate the spatial and temporal characteristics of these hippocampally anchored post-encoding neocortical modulations. Eighty-nine adults participated in an experiment consisting of interleaved memory task- and resting-state periods. As expected, we observed increased post-encoding functional connectivity between hippocampus and individually localized neocortical regions responsive to stimulus categories encountered during memory encoding. Post-encoding modulations were however not restricted to stimulus-selective cortex, but manifested as a nearly system-wide upregulation in hippocampal coupling with all major functional networks. The spatial configuration of these extensive modulations resembled hippocampal-neocortical interaction patterns estimated from active encoding operations, suggesting hippocampal post-encoding involvement by far exceeds reactivation of perceptual aspects. This reinstatement of encoding patterns during immediate post-encoding rest was not observed in resting-state scans collected 12 hours later, nor in control analyses estimating post-encoding neocortical modulations in functional connectivity using other candidate seed regions. The broad similarity in hippocampal functional coupling between online memory encoding and offline post-encoding rest suggests reactivation in humans may involve a spectrum of cognitive processes engaged during experience of an event. Significance statementStabilization of newly acquired information into lasting memories occurs through systems consolidation - a process which gradually spreads the locus of memory traces from hippocampus to more distributed neocortical representations. One of the earliest signs of consolidation is the upregulation of hippocampal-neocortical interactions during periods of awake rest following an active encoding task. We here show that these modulations involve much larger parts of the brain than previously reported in humans. Comparing changes in hippocampal coupling during post-encoding rest with those observed under active encoding, we find evidence for encoding-like hippocampal reinstatement throughout cortex during task-free periods. This suggests early systems consolidation of an experience involves reactivating not only core sensory details but multiple additional aspects of the encoding event.

neuroscience↗

bioRxiv2021

Whole-brain connectivity during encoding: age-related differences and associations with cognitive and brain structural decline

There is a limited understanding of age differences in functional connectivity during memory encoding. In the present study, a sample of cognitively healthy adult participants (n=488), a subsample of whom had longitudinal cognitive and brain structural data spanning 8 years back, underwent fMRI while performing an associative memory encoding task. We investigated 1) age changes in whole-brain connectivity during memory encoding; whether 2) encoding connectivity patterns overlap with the activity signatures of specific cognitive processes and whether 3) connectivity changes associated with memory encoding related to longitudinal brain structural and cognitive changes. Age was associated with decreased intranetwork connectivity and increased connectivity during encoding. Task-connectivity between mediotemporal and posterior parietal regions - which overlapped with areas involved in mental imagery - was related to better memory performance only in older age. The connectivity patterns supporting memory performance in older age reflected preservation of thickness of the medial temporal cortex. These investigations collectively indicate that functional patterns of connectivity should be interpreted in accordance with a maintenance rather than a compensation account.

neuroscience↗

bioRxiv2018

Continuity and discontinuity in human cortical development and change from embryonic stages to old age

The human cerebral cortex is highly regionalized. We aimed to test whether principles of regionalization could be traced from embryonic development throughout the human lifespan. A data-driven fuzzy-clustering approach was used to identify regions of coordinated longitudinal development of cortical surface area (SA) and thickness (CT) over 1.5 years (n = 301, 4-12 years). First, the SA clusters were compared to patterns from embryonic cortical development. The earliest sign of cortical regionalization is the emergence of morphometric gradients in the cerebral vesicles, with a major gradient running along the anterior-posterior (AP) axis. We found that the principal divide for the developmental SA clusters extended from the inferior-posterior to the superior-anterior cortex, corresponding to the embryonic morphometric AP gradient. Second, embryonic factors showing a clear AP gradient were identified, and tests revealed significant differences in gene expression of these factors between the anterior and posterior clusters. Further, each identified developmental SA and CT cluster showed distinguishable lifespan trajectories in a larger longitudinal dataset (4-88 years, 1633 observations). This means that regions that developed together also changed together throughout life, demonstrating continuity in regionalization of cortical changes. The AP divide in SA development also characterized genetic patterning obtained in an adult twin sample, but otherwise regionalized CT development adhered more to the genetic boundaries. Finally, SA and CT clusters showed differential relationships to cognitive functions. In sum, the results suggest that development of cortical regionalization is a continuous process from the embryonic stage throughout human life.\n\nSignificance statement (120 words)The protomap and the radial unit theories of brain development have shown that graded expression patterns of several factors are responsible for shaping the ultimately highly partitioned and specialized neocortical landscape. The present study shows that the major anterior-posterior gradient of embryonic development can be detected in the regional cortical expansion profiles of children. The study further demonstrates that brain regions that develop together during childhood also tend to change together throughout the lifespan. This suggests that regional cortical development is a continuous process through the entire life, and that early-life factors have life-long impacts on this process.

neuroscience↗