Question

discuss the neural basis of waking behavior?

Describe the three tests that make use of a hidden platform in a swimming pool to examine memory in mice.

Answer 1

Overview of sleep and wake states:

Neurobiologist often defines wakefulness as a spectrum of behavioral states during which a creature exhibits voluntary motor activation and is responsive to internal stimuli and external stimuli. Consciousness has been little studied in animals, but it is a critical topic in clinical research.

When one enters NREM sleep, consciousness get faded, and in the deepest stages, sensory gating can block all but the strongest and most salient stimuli. During REM sleep, vivid, emotional, and story-like dreams are common, w hich are accompanied by rapid eye movements and fluctuations in heart rate and respiration.

The electroencephalogram (EEG) and electromyogram (EMG) are excellent biomarkers of sleep/wake states. During wake, the EEG shows low amplitude, fast frequencies, and lastly the EMG shows variable amounts of muscle activity. During NREM sleep, the EEG is dominated by slower frequencies in the delta (0–4 Hz) and theta (4–7 Hz) ranges, and prolonged periods of wake are usually followed by large amounts of NREM sleep with especially high delta activity. In humans, the EEG during REM sleep shows low amplitude, fast activity much like that of wake with a modest amount of theta activity. In rodents, the cortical EEG during REM sleep shows abundant theta activity that arises from the underlying dorsal hippocampus. Muscle activity is strongly suppressed during REM sleep, preventing the enactment of dreams.

Regulation of wake:

About 100 years ago, when an epidemic of encephalitis lethargica swept through Europe, and affected patients would often sleep more than 20 hours/day for months on end. The Viennese neurologist Constantin von Economo discovered that these patients often had lesions in the midbrain and posterior hypothalamus, and he proposed that these regions contain vital wake-promoting circuitry. Moruzzi and Magoun later then showed that electrical stimulation of the reticular formation in anesthetized cats shifts the EEG from the slow activity typical of anesthesia to fast activity similar to that seen during wake. These observations fit well with the prevailing idea that the reticular formation integrates sensory information and then drives generalized arousal and motor responses. However, over the last decades, the idea of undifferentiated reticular neurons has faded as researchers established that the major influences on arousal arise from neurochemically distinct systems.

The brainstem control of state stability:

The reciprocal inhibitory exchange between the major ascending monoaminergic arousal groups and the sleep-inducing VLPO acts as a feedback loop; when monoamine nuclei discharge intensively during wakefulness, they inhibit the VLPO, and when VLPO fire rapidly during sleep, block the discharge of the monoamine cell groups. This relationship is described as a bistable, “flip-flop” circuit, in which the two halves of the circuit strongly inhibit each other to produce two stable discharge patterns – on or off​
. Intermediate states that might be partially “on and off” are resisted. This model helps clarify why sleep-wake transitions are relatiely brupt and mammals spend only about 1% to 2% of the day in a transitional state. Hence, changes between sleep and arousal occur infrequently and rapidly. As will be described below, the neural circuitry forming the sleep switch contrasts with homeostatic and circadian inputs, which are continuously and slowly modified.