Behavioral state development in infants

University Of Iowa, Iowa City IA

Investigators

Linked publications & trials

Abstract

DESCRIPTION (provided by applicant): Sleep occupies one-third of our adult lives and yet its function is still not known. In infants, sleep is even more prominent, as are the spontaneous myoclonic twitches that are a defining feature of active (or REM) sleep. Over the past decade, research in the Principal Investigator's laboratory has helped dispel the notion - which held sway until recently - that the brain plays no role in the control of infant sleep. Moreover, it is now widely accepted that sensory feedback (i.e., reafference) from twitching is closely monitored at all levels of the neuraxis. Of particular importance for this application is the recent discovery of oscillatory events-called spindle-bursts (SBs)-that are produced in primary sensory cortices in response to endogenously and exogenously generated sensory stimulation. It is thought that twitching, its associated reafference, and cortical SBs participate together in the development and maintenance of topographic organization. The Principal Investigator's laboratory has been engaged in this effort by monitoring neurophysiological activity in unanesthetized newborn rats as they cycle spontaneously between sleep and wakefulness and respond to specific peripheral tactile and proprioceptive stimulation. This application addresses two broad aims. First, a transient period during the first postnatal week in rats has been discovered when corpus callosotomy disinhibits spontaneous cortical activity and when recovery of function after callosotomy is possible. It is hypothesized that sleep-related twitching contributes to this recovery of function, just as it contributes to normal development. To test this hypothesis, neurophysiological and neuropharmacological approaches will be used, including the novel application of amperometry to unanesthetized infant rats for the measurement of real-time extracellular changes in cortical choline, glutamate, and GABA levels in relation to behavioral state, myoclonic twitching, and peripheral stimulation. Second, recent work suggests that SBs are differentially regulated depending on whether they are produced spontaneously (during active sleep) or evoked by peripheral proprioceptor stimulation. Because the ability of individuals to differentiate self-produced from externally produced sensory input relies upon the production of an efference copy, it is important to identify in newborn rats the neural circuitry that transmits spontaneous and evoked sensory information to somatosensory cortex. This aim will be accomplished using a combination of methods, including surface EEG, amperometry, and selective unilateral inactivation of brain regions in the midbrain and forebrain. Preliminary results from the Principal Investigator's laboratory now demonstrate the feasibility of using amperometry in unanesthetized infant rats. The NIH Blueprint for Neuroscience emphasizes the need for more basic research to understand neurodevelopment, neurodegeneration, and neuroplasticity. This application is compatible with the Blueprint, focusing as it does on sleep, neural function, and brain plasticity across early infancy under normal conditions and after neural insult. Moreover, the approach that informs this work is contributing to a fundamental reconceptualization of infant sleep that will soon provide the foundation for a broader understanding of the function of sleep in both infants and adults.