Related by context. Frequent words. (Click for all words.) 65 REM sleep 61 circadian 60 circadian rhythm 58 sleepiness 57 circadian rhythms 56 alertness 54 norepinephrine 53 arousal 53 melatonin 53 insomnia 52 drowsiness 52 drowsy 52 cognition 51 serotonin 51 cognitive function 51 daytime sleepiness 50 adenosine 50 ADHD symptoms 50 levodopa 49 sleep 49 brain circuitry 48 awakenings 48 Melatonin 48 dopamine 48 methylphenidate 48 physiologic 47 neurogenesis 47 cognitive functioning 47 GABA 47 synaptic 47 cortisol 46 metabolism 46 circadian clock 46 satiety 46 leptin 46 insulin secretion 46 impulsive behavior 46 Dopamine 46 cortisol levels 46 depressive 46 physiological 46 narcolepsy 45 secretion 45 fluoxetine 45 sleep disturbances 45 sleep deprived 45 hallucinations 45 metabolic 45 hormonal 45 awake 45 visual cortex 45 cognitive functions 44 ghrelin 44 Serotonin 44 erectile function 44 plasticity 44 chronic insomnia 44 sleeplessness 44 stress hormone cortisol 44 sleep disorders 44 glucose metabolism 44 restlessness 44 neurons 44 cortical 44 acetylcholine 44 cognitive deficits 43 BDNF 43 neurotransmitter 43 basal ganglia 43 benzodiazepine 43 menstrual cycle 43 gabapentin 43 irritability 43 somnolence 43 neurotransmitters 43 anti depressant 43 neurobiological 43 cognitive 43 hyperactivity 43 antidepressant 43 stress hormones 43 insomniac 43 erections 43 striatum 43 neuronal 42 psychosis 42 minimally conscious 42 blood glucose levels 42 brainwaves 42 psychotic symptoms 42 antipsychotic 42 schizophrenia 42 tryptophan 42 cortex 42 neurones 42 hippocampus 42 opioid 42 biological clocks 42 Lunesta 42 doze 42 Ritalin