4/9/15 – Lecture 21 – Sleep and circadian Rhythms- Goal: to establish what sleep is and why it is important- Sleep – an actively produced state characterized by reduced sensory awareness and motor activityo Sleep is not unconsciousness – sleep is very different from being knocked unconscious, fainting, coma, and hibernationo Sleep is not passive – there are active neural circuits involved in “falling” and staying asleepo Sleep is not homogeneous – there are many different stages to sleep Studying Sleep- Electrooculography (EOG) – measures movement of the eyes- Electromyography (EMG) – measures electrical activity of the muscles, particularly in the neck- Electroencephalography (EEG) – measures electrical activity in the braino Wakefulness – characterized by small and rapid EEG waves High EOG activity High EMG activityo “Slow wave” sleep – Non Rapid Eye Movement Sleep – characterized by larger, slower EEG waves No EOG activity Less EMG activity- Larger, slower EEG waves (theta and delta waves), less EMG, no EOG- Accounts for most (6-8 hours) of sleep in adults- Stages 3 and 4 are the deepest stages of sleep and are the hardest to wake you up during- Characterized by the most movement – flailing, tossing and turning, even sleep walking and somniloquy- Much less dreaming but night terrors in childreno WE DO DREAM IN NREM SLEEP, they are just more fragmented and less memorableo “Fast wave” sleep – Rapid Eye Movement Sleep – a return to the small and rapid EEG waves of wakefulness High EOG activity No EMG activity- Short, rapid EEG, no EMG, high EOG- Muscles occasionally twitch but large movements arenot common – motor neuron activity is inhibited during REM sleep- Accounts for about 2 hours of sleep in adults interspersed between bouts of NREM sleepo Amount increases as the sleep period increases- Is characterized by much more dreaming and more vivid, narrative dreamso Is REM sleep Necessary? Yes- Nearly all mammals and many birds appear to have REM sleep- If deprived of REM sleep, a person experiences “REMrebound” – increased tendency to go into REM sleep and have more REM sleep per sleep session No- Some animals – whales of example – seem to have very little REM if any sleepo Only sleep with half of their brain at a time- Nearly all anti-depressant medications suppress REMsleep partly or completely and patients who take them go months without REM sleepo Dreams Everyone dreams, they typically dream multiple times a night, and dreams last longer as the sleep session progresses All mammals and birds appear to dream or at least have REMsleep Dreams appear to take place in real time Sensory information can occasionally be incorporated into dreams Dreams often contain conflict or negative emotional stateso Why do we dream?? Freudian Interpretation – dreams are a manifestation of our subconscious wishes, desires and fears – activity of the dorsolateral prefrontal cortex decreases and the amygdala increases during sleep Dreams as Memory Pruning and Consolidation – activity of the hippocampus and the sensory association cortices are increased during dreaming in ways that many facilitate LTP between these areas Dreams as a way to rehearse responses or develop solutions to difficult, dangerous, or aversive situations – activity of the anterior cingulate cortex and amygdala is increased during dreaming Dreams as Meaningless Brain Activity – epileptics having seizures and schizophrenics having hallucinations also report similar experiences to dreamingo Why do we sleep? Sleep as energy conservation or replenishment Sleep as a restorative or anabolic process – sleep promotes wound healing, growth, and glymphatic flow Sleep as a critical component of brain function – sleep promotes memory consolidation, emotion regulation, and cognitive functiono Sleep and Bain Function Sleep appears to be important in the consolidation of explicit and implicit memory- NREM sleep – spatial and explicit memory- REM sleep – implicit memoryo Sleep as a means to solve problemso Sleep improves mood and blunts emotionallytraumatic memories Neurobiology of Wakefulness and Sleep- 4 main brain areas involved in Wakefulness and Sleepo Reticular Activating System (RAS) – group of nuclei in the brainstemo Basal Forebrain – group of neurons in the forebrain that release acetylcholine Receive sensory input from spinal cord and lower brain Sends axons to the hypothalamus, thalamus, and cerebral cortex, exciting neurons in these areas by releasing aminergicneurotransmitters like norepinephrine, histamine, and dopamineo Hypothalamus Lateral Hypothalamus – releases orexin and promotes wakefulness and arousal VLPO Hypothalamus – releases GABA (hyperpolarizes neurons and decreases action potentials) and promotes sleepo Cerebral Cortex Critical for motor behavior, cognition, and sensory perceptionas part of wakefulness Arousal or wakefulness is associated with increased electricalactivity of cortical neurons – increased action potential firing Excitatory neurotransmitters that depolarize neurons and increase electrical excitability increase arousal and wakefulness- Neurobiology of Wakefulnesso Sensory information is sent to the reticular activating system (RAS)o Sensory info activates RAS neurons which sends axons to the Lateral Hypothalamus, thalamus, and cortexo RAS, LH, and basal forebrain neurons release excitatory neurotransmitters (like acetylcholine, norepinephrine, serotonin, dopamine, histamine and orexin) onto neurons of the thalamus and cortexo Increased excitation of cortical neurons results in increased arousal and wakefulness- Neurobiology of Falling Asleepo Sensory information decreases – noise, other stimuli decreases whenwe go to bed, which decreases activity of the reticular activating systemo Light Levels decrease – this increases activity of VLOP hypothalamus neurons, which secrete GABA onto neurons of the RAS and LH, inhibiting their firingo Adenosine levels in the brain increase – due to metabolism during the day as ATP is broken down to ADP, to AMP, and to adenosine and inhibit activity of the basal forebrain Circadian Rhythms- Daily cycles of physiological, metabolic, biochemical and behavioral processes(sleep-wake cycles, eating, hormone release, temp)- Typically set to around but not necessarily exactly 24 hours- Cycles are