Endogenous Rhythms and Biological Clocks

Endogenous Rhythms

• Endogenous circannual rhythm: Internal calendar preparing a species for annual seasonal changes.
• Endogenous circadian rhythm: Internal rhythms lasting about a day, including wakefulness and sleepiness.
• Circadian rhythm in humans: Self-generated duration of about 24 hours, impacting eating, drinking, hormone secretion, and mood. Body temperature also fluctuates, typically 36.7°C at night and 37.2°C late afternoon/early evening. Teenagers experience increased positive mood from waking to late afternoon, then a slight decrease.
• Zeitgeber: External stimulus (primarily light) needed to reset circadian rhythm.

Setting and Resetting the Biological Clock

• Light is the dominant zeitgeber for land animals.
• Incomplete light/dark cycles affect alertness and sleep quality.
• Individuals using external factors like noise or temperature can also reset their circadian rhythm.
• Disruption of circadian rhythm through daylight savings time and shift work can cause inefficiency & insomnia
• Repeated circadian rhythm adjustments increase cortisol levels, potentially damaging the hippocampus and affecting memory.

Stages of Sleep and Brain Mechanisms

• Sleep: Decreased brain response to stimuli.
• Coma: Prolonged unconsciousness with low brain activity.
• Vegetative State: Alternating between sleep/moderate arousal, lacking awareness.
• Minimally Conscious State: Occasional purposeful actions, limited speech comprehension.
• Brain Death: Absence of brain activity and response.

Stages of Sleep

• EEG: Electroencephalography measures electrical brain activity.
• Polysomnograph: Combination of EEG and eye-movement records.
• Stage 1 Sleep: Irregular, jagged, and low-voltage waves; light sleep.
• Stage 2 Sleep: Includes sleep spindles (burst of 12-14 Hz waves) and K-complexes (sharp, high amplitude waves); intermediate sleep.
• Stages 3 & 4 Sleep (Slow-Wave Sleep (SWS)): Slow, large-amplitude waves; deep and restorative sleep.
• REM Sleep (Rapid Eye Movement): Brain is active while muscles are relaxed. Associated with dreaming.

Brain Structures of Arousal and Attention

• Reticular formation: Neural structure from medulla to forebrain influencing arousal.
• Pontomesencephalon: Portion of the reticular formation promoting cortical arousal.
• Locus coeruleus: Brain structure releasing norepinephrine to enhance arousal in response to important events - dormant during sleep.
• Hippothalamus: Areas releasing histamine (excitatory effects) and orexin (critical for alertness) are vital in waking and sleep.
• Basal forebrain: Area releasing GABA to reduce neural activity and promote sleep.

Sleep and the Inhibition of Brain Activity

• During sleep, body temperature and metabolic rate slightly decrease.
• GABA plays a significant role in lowering synaptic activity, leading to sleep.
• Sleepwalking and sleep talking can happen in certain sleep stages.

Brain Mechanisms of Wakefulness, Arousal, and Sleep

• Sleep is controlled by a complex interaction of brain regions which includes the reticular formation, and limbic system.
• Different parts of the brain are very active during various stages of sleep.
• Sleep problems can be located in specific parts and structures in the brain.

Brain Mechanisms Controlling Attention

• Bottom-up Process: Reaction to a stimulus
• Top-down Process: Intentional attention (e.g., searching for someone in a crowd).
• Brain areas play significant roles in controlling attention.

The Hippocampus and the Striatum

• Short Term Memory : Related to recent events
• Long Term Memory: Related to more distant events
• Hippocampus is crucial for declarative memory, but other structures like the striatum are essential for procedural memory (or habits)
• Declarative Memories: Include episodic memory (personal experiences) and semantic memory (general knowledge).
• Procedural Memories : Related to habits.
• Parts of the brain, including basal ganglia and other areas, are heavily involved in memory, and damage/problems in these structures can result in memory loss.

Sleep Disorders

• Insomnia: Inability to sleep or maintain sleep.
• Sleep Apnea: Inability to breathe during sleep.
• Night Terrors: Abrupt and anxious awakenings from NREM sleep.
• Sleepwalking: Often occurs during stages 3 or 4 early in the night.
• Narcolepsy: Disorder characterized by excessive daytime sleepiness.
• Periodic Limb Movement Disorder: Involuntary movements of the legs and arms, primarily during NREM sleep.

Consciousness and Unconscious Processes

• Conciousness: Awareness of self and the environment.
• Different views of the mind-body problem exist.
• Consciousness depends on brain activity, especially widespread activation throughout the cortex.
• Certain brain regions are involved in different types of consciousness; the brain operates as a network of interconnected brain regions.

Cognitive Functions-Laterality and Language

• Brain Has Two Hemispheres: Each controls the opposite side of the body.
• Lateralization: Specialization of functions in each hemisphere. Language is primarily localized in the left hemisphere (in most people).
• Corpus Callosum: Bundle of axons connecting the two hemispheres and allowing communication.
• Split Brain Patients: Individuals whose corpus callosum is severed; their hemispheres show independent actions.
• Visual and Auditory Connections: Sensory information is typically routed to the opposite hemisphere.

Cognitive Functions-Visual and Auditory Connections

• Information from the right visual field is relayed to the left hemisphere and from the left visual field to the right hemisphere.
• Sound from each side of the head is routed to both hemispheres, but each ear sends information to both hemispheres