The ability to process in parallel multiple forms of sensory information, and link sensory-sensory associations to behavior, presumably allows for the opportunistic use of the most reliable and predictive sensory modalities in diverse behavioral contexts. Evolutionary considerations indicate that such processing may represent a fundamental operating principle underlying complex sensory associations and sensory-motor integration. Here, we suggest that animal navigation is a particularly useful model of such opportunistic use of sensory and motor information because it is possible to study directly the effects of memory on neural system functions. First, comparative evidence for parallel processing across multiple brain structures during navigation is provided from the literatures on fish and rodent navigation. Then, based on neurophysiological evidence of coordinated, multiregional processing, we provide a neurobiological explanation of learning and memory effects on neural circuitry mediating navigation.
Sleep spindles are highly synchronous oscillations (7-14 Hz) occurring during slow wave sleep as sporadic events or triggered by the sleep slow oscillation (0.6-0.8 Hz). Although recent works have shown a functional link between spindles and learning or memory consolidation processes, their impact on synaptic transmission is largely unexplored. We studied the ability of a neuronal firing pattern underlying spindles recorded in vivo to induce activity-dependent synaptic plasticity in layer V pyramidal cells in vitro. A spindle stimulation pattern (SSP) was extracted from the intracellular trace of a neuron during a slow oscillation upstate that was recorded within the primary somatosensory cortex of a cat anesthetized with ketamine-xylazine, which is known to induce a sleep-like state. Since the cortical sleep slow oscillation works as a sleep spindles pacemaker, in order to mimic their recurrence the SSP was repeated every 1.5 s (0.6 Hz). Whole-cell patch-clamp recordings were obtained from layer V pyramidal cells of rat primary somatosensory cortex visualized by infrared microscopy, and composite EPSPs were evoked within layers II-III. Simultaneous trains of EPSPs and action potentials (AP) triggered by the SSP induced an NMDAr-dependent short-term potentiation (STP) and a L-type Ca++ channel-dependent long-term potentiation (LTP). The magnitude of both the STP and the LTP depended on the number of applied spindle trains. In contrast, spindle trains of EPSPs alone induced long-term depression (LTD). A homogeneous firing pattern with the same frequency as the mean of the original spindle train left synapses unaltered as well as a mirror SSP and a shuffled SSP. On the contrary a synthetic spindle pattern consisting of repetitive spike bursts at 10 Hz induced both STP and LTP. We conclude that sleep spindles can change strength at excitatory neocortical synapses on different time-scales and in different directions according to a Hebbian rule. This may account for the proposed role of sleep spindle for learning and memory consolidation. The locus coeruleus (LC) of the brainstem is the major noradrenergic nucleus in the central nervous system. Its connections extend to the thalamus, hippocampus and the entire neocortex. One main function of the LC is the modulation of the arousal state, with it being in a state of high tonic activity during wakefulness and shut off during REM sleep. LC activity can increase the signal-to-noise ratio of neurons and thus promote information processing. Through its hippocampal connections, it may also modulate memory function or synaptic potentiation. Interestingly, during SWS, which is a state of low arousal, the LC is still active, although at a lower rate than during wakefulness. In a series of experiments, we investigated whether this activity is related to the consolidation of memories during sleep. Subjects (healthy, young males) had to perform an odour recognition task, which required them to learn six different unfamiliar odours and, 24-h later, to recognize them among twelve od...
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