Biomedical subjects

Elizabeth Hennevin

Publications and source records attributed to Elizabeth Hennevin.

5 recordsLinked to original sources

PubMed2006

Neural representations during sleep: from sensory processing to memory traces.

In the course of a day, the brain undergoes large-scale changes in functional modes, from attentive wakefulness to the deepest stage of sleep. The present paper evaluates how these state changes affect the neural bases of sensory and cognitive representations. Are organized neural representations still maintained during sleep? In other words, despite the absence of conscious awareness, do neuronal signals emitted during sleep contain information and have a functional relevance? Through a critical evaluation of the animal and human literature, neural representations at different levels of integration (from the most elementary sensory level to the most cognitive one) are reviewed. Recordings of neuronal activity in animals at presentation of neutral or significant stimuli show that some analysis of the external word remains possible during sleep, allowing recognition of behaviorally relevant stimuli. Event-related brain potentials in humans confirm the preservation of some sensory integration and discriminative capacity. Behavioral and neuroimaging studies in humans substantiate the notion that memory representations are reactivated and are reorganized during post-learning sleep; these reorganisations may account for the beneficial effects of sleep on behavioral performance. Electrophysiological results showing replay of neuronal sequences in animals are presented, and their relevance as neuronal correlates of memory reactivation is discussed. The reviewed literature provides converging evidence that structured neural representations can be activated during sleep. Which reorganizations unique to sleep benefit memory representations, and to what extent the operations still efficient in processing environmental information during sleep are similar to those underlying the non-conscious, automatic processing continually at work in wakefulness, are challenging questions open to investigation.

Animals↗

PubMed2005

Fear conditioning-induced plasticity in auditory thalamus and cortex: To what extent is it expressed during slow-wave sleep?

After fear conditioning to a tone, rats received nonawakening presentations of the tone alone during slow-wave sleep (SWS) episodes. Multiunit activity was recorded in the medial part of the medial geniculate (MGm) and in the primary auditory cortex (ACx). Although tone-evoked responses were increased in MGm and ACx during the 3 conditioning sessions, group data failed to show any significant changes during SWS. Nonetheless, the few recordings (5/29) that exhibited the strongest conditioned responses during wakefulness expressed enhanced responding during SWS. Compared with previous data obtained in MGm during paradoxical sleep, associative plastic changes were less easily expressed during SWS. These results are discussed with regard to functional changes that occur in the thalamocortical system across vigilance states.

Action Potentials↗

PubMed2003

The cholinesterase inhibitor DFP facilitates the expression of paradoxical sleep (PS) propensity in rats subjected to short-term PS deprivation.

Short-term paradoxical sleep (PS) deprivation was used to examine the effects of chronic exposure to subtoxic doses of the cholinesterase inhibitor diisopropylfluorophosphate (DFP) on PS regulation. Rats were injected once daily with DFP (0.2 mg/kg per day; s.c.) for 11 consecutive days; control rats received a daily injection of oil vehicle. The experiment was conducted on the 10th and 11th days of treatment, when brain cholinesterase inhibition induced by DFP exposure was maximal. On the 10th day, an 8-h baseline recording was carried out. On the 11th day, a 6-h PS deprivation was carried out by manually awaking rats each time they showed polygraphic signs of PS; recordings were then continued for another 2 h to examine recovery sleep. During deprivation, though they slept less than controls, DFP-treated rats made more attempts to enter PS. After deprivation, their PS rebound had an overall amount comparable to that of the controls, but its time course was shortened: whereas PS elevation was manifested through the 2 h of recovery in the control group, it occurred only during the first hour in the DFP group. These results demonstrate that chronic, low-level DFP exposure facilitated the expression of the PS propensity that accumulated as a result of PS deprivation: it enhanced the tendency for PS during deprivation; it accelerated the rate of compensatory PS expression after deprivation. They support the hypothesis that DFP promotes PS initiation by increasing cholinergic transmission.

Animals↗

PubMed2002

Muscimol diffusion after intracerebral microinjections: a reevaluation based on electrophysiological and autoradiographic quantifications.

Intracerebral muscimol injection is widely used to inactivate discrete brain structures during behavioral tasks. However, little effort has been made to quantify the extent of muscimol diffusion. The authors report here electrophysiological and autoradiographic results obtained after muscimol injection (1 microg/microl) either into the nucleus basalis magnocellularis (0.1-0.4 microl) or into the thalamic reticular nucleus (RE, 0.05-0.1 microl). In 52 rats, multiunit recordings were collected either in the RE or in the auditory thalamus during the 2 h following muscimol injection. Decreases in neuronal activity were observed up to 3 mm from the injection site; their time of occurrence was a function of the distance between the injection and recording sites. Because these decreases cannot be explained by physiological effects, they likely reflected muscimol diffusion up to the recording sites. Autoradiographic studies involved 25 rats and different experimental conditions. Optical density (OD) measures indicated that after a survival time of 15 min, a 0.05 microl injection produced a labeled area of 5.25 mm(2) at the injection site and a rostrocaudal labeling of 1.7 mm. Increasing the survival time to 60 min, or increasing the injected volume to 0.1 microl, systematically led to a larger labeled area at the injection site (8-12 mm(2)) and to a larger rostrocaudal diffusion (2.0-2.5 mm). Direct quantifications of radioactivity by a high-resolution radioimager validated the OD measures and even indicated a larger muscimol diffusion (up to 3.25 mm). Thus, these data point out that muscimol diffusion after intracerebral microinjection is larger than usually supposed. The relationships between these results and those obtained in behavioral studies are discussed.

Animals↗

PubMed2002

Appetitive conditioning-induced plasticity is expressed during paradoxical sleep in the medial geniculate, but not in the lateral amygdala.

This study examined whether neurons in the medial division of the medial geniculate (MGm) and the dorsal part of the lateral amygdala (LAd) express learning-induced plasticity in paradoxical sleep (PS) after appetitive conditioning, as they do in PS after fear conditioning. Rats received tone-food pairings in 3 sessions. After each session, the tone was presented at a nonawakening intensity during PS. Multiunit activity was simultaneously recorded in MGm and LAd. During waking, increases in tone-evoked discharges developed in MGm and LAd; however, as training continued, they lessened in LAd, but not in MGm. During PS, conditioned tone responses were expressed in MGm, but not in LAd. Thus, these results demonstrate dissociation of MGm and LAd plasticity. Moreover, compared with fear conditioning results, they suggest that expression of amygdalar plasticity in PS depends on the emotional salience of the stimulus.

Acoustic Stimulation↗