Biology subjects

Tort, A. B. L.

Publications and source records attributed to Tort, A. B. L..

4 recordsLinked to original sources

bioRxiv2022

Hippocampal delta oscillations entrain neuronal activity, modulate gamma amplitude and convey information about running speed on a treadmill

Locomotion has long been associated with rhythmic oscillations in the rat hippocampus. Running speed and acceleration affect the spectral density at the theta (6-10 Hz) and gamma (30-150 Hz) bands and the rhythmic entrainment of neuronal activity. However, less is known about other oscillatory rhythms. Recent studies have shown that oscillatory activity in the delta (1-4 Hz) band also relates to locomotion in stationary conditions, such as running on a treadmill or in a running wheel. To further investigate the effects of stationary running on hippocampal oscillations, we recorded CA1 local field potentials and neuronal activity while rats ran at different speed protocols on a treadmill. We found a remarkable oscillatory activity at 2 Hz that was strongly modulated by running speed. Delta power and peak frequency were highest at the fastest running speed, both in constant and progressively increasing speed protocols. Delta and theta oscillations co-occurred and showed independent relationships in their instantaneous power and frequency. Moreover, the delta phase modulated the amplitude of low-gamma (20-50 Hz) oscillations and the spiking activity of putative pyramidal neurons in a speed-dependent manner. Finally, spectral components in the delta frequency range, but not theta, predicted running speed using a naive Bayes classifier. In summary, our study shows that locomotion-related delta oscillations convey information about stationary running speed and coordinate hippocampal rhythmic activity in a speed-dependent manner. Statement of significanceTheta and gamma oscillations are hallmarks of rhythmic activity in the rat hippocampus during locomotion and exploratory behaviors, but less is known about other oscillatory rhythms. This study shows the emergence of delta ([~]2 Hz) oscillations in the dorsal CA1 of rats running on a treadmill. Locomotion-related delta oscillations are independent of the concomitant theta activity and convey information about running speed. Delta waves modulate low-gamma oscillations and the spiking activity of pyramidal neurons in a speed-dependent way. These results suggest that oscillatory activity in the delta band aids rhythmic coordination during stationary locomotor behaviors.

neuroscience↗

bioRxiv2019

Respiration competes with theta for modulating parietal cortex neurons

Recent work has shown that nasal respiration entrains local field potential (LFP) and neuronal activity in widespread regions of the brain. This includes non-olfactory regions where respiration-coupled oscillations have been described in different mammals, such as rodents, cats and humans. They may, thus, constitute a global signal aiding interregional communication. Nevertheless, the brain produces other widespread slow rhythms, such as theta oscillations, which also mediate long-range synchronization of neuronal activity. It is completely unknown how these different signals interact to control neuronal network activity. In this work, we characterized respiration- and theta-coupled activity in the posterior parietal cortex of mice. Our results show that respiration-coupled and theta oscillations have different laminar profiles, in which respiration preferentially entrains LFPs and units in more superficial layers, whereas theta modulation does not differ across the parietal cortex. Interestingly, we find that the percentage of theta-modulated units increases in the absence of respiration-coupled oscillations, suggesting that both rhythms compete for modulating parietal cortex neurons. We further show through intracellular recordings that synaptic inhibition is likely to play a role in generating respiration-coupled oscillations at the membrane potential level. Finally, we provide anatomical and electrophysiological evidence of reciprocal monosynaptic connections between the anterior cingulate and posterior parietal cortices, suggesting a possible source of respiration-coupled activity in the parietal cortex.

neuroscience↗

bioRxiv2018

Reactivation of time cell sequences in the hippocampus

The temporal order of an experience is a fundamental property of episodic memories, yet the mechanism for the consolidation of temporal sequences in long-term memory is still unknown. A potential mechanism for memory consolidation depends on the reactivation of neuronal sequences in the hippocampus. Despite abundant evidence of sequence reactivation in the formation of spatial memory, the reactivation of hippocampal neuronal sequences carrying non-spatial information has been much less explored. In this work, we recorded the activity of time cell sequences while rats performed multiple 15-s treadmill runnings during the intertrial intervals of a spatial alternation memory task. We observed forward and reverse reactivations of time cell sequences often occurring during sharp-wave ripple events following reward consumption. Surprisingly, the reactivation events specifically engaged cells coding temporal information. The reactivation of time cell sequences may thus reflect the organization of temporal order required for episodic memory formation.

neuroscience↗

bioRxiv2017

Parallel Occurrence Of Theta And Respiration-Coupled Network Oscillations Throughout The Mouse Brain

Slow brain oscillations are usually coherent over long distances and are thought to constitute a means to link distributed cell assemblies. In mice, theta oscillations (4-12 Hz) stand as one of the most studied global slow rhythms. Previous research has suggested that theta takes part in interregional communication required for cognitive functions. However, mice often breathe at theta frequency, and we have recently reported that nasal respiration leads to synchronous network oscillations that are independent of theta. Namely, we showed that respiration-coupled oscillations occur in the hippocampus, prelimbic cortex, and parietal cortex, suggesting that, as theta, respiration-coupled oscillations are also global. In the present work, we sought to extend these findings by tracking respiration while simultaneously recording local field potentials from 15 brain regions of freely moving mice during exploration and REM sleep. We report that respiration-coupled rhythms can be detected in parallel with theta in widespread neocortical regions, from prefrontal to visual areas, and also in subcortical structures such as the thalamus, amygdala and ventral hippocampus. Though both rhythms occur simultaneously, respiration-coupled oscillations are more dominant in frontal regions while theta oscillations prevail in more caudal networks. We conclude that respiration-coupled oscillations are a global brain rhythm suited to entrain distributed networks into a common regime. This pattern might have escaped attention in previous studies due to the absence of respiration monitoring, its similarity with theta oscillations, and its highly variable peak frequency. It should, however, be considered as a widespread signal and potential mechanism of long-range network communication.

neuroscience↗