Bio psych exam 3

endogenous circadian rhythms

• Internal mechanisms that operate on an approximately 24 hour cycle

• Animals generate endogenous 24 hour cycles of wakefulness and sleep

Chronotypes

• Cycles can differ between people and lead to different patterns of wakefulness and alertness

• Night “owls” vs morning “larks”

• The cycles change somewhat as a function of age

Chronotypes (by age and sex)

• Adolescents, all stay up late and get up late, more so males than females.

• Older adults prefer to go to bed early and get up early

What is the purpose of the circadian rhythm

• The purpose of the circadian rhythm is to keep our internal workings in phase with the outside world

• The human circadian clock generates a rhythm slightly longer than 24hrs (for most people; but some will run 25 -27 hours long) when no external cues reset it (“free -running”)

Zeitgeber

• German for “time giver”; refers to any stimulus that entrains (updates & calibrates) the circadian rhythm

• Examples: sunlight, tides, exercise, meals, arousal of any kind, meals, temperature of environment, etc.

• But LIGHT is the primary zeitgeber for humans.

Jet lag ; phase delay

Pushing our circadian rhythm back by falling asleep later than usual

Jet lag ; phase advance

pushing our circadian rhythm up by falling asleep sooner than usual

Suprachiasmatic nucleus (SCN)

The suprachiasmatic nucleus (SCN) is part of the hypothalamus and the main control center of the circadian rhythms of sleep and temperature

• Located above the optic chiasm

• SCN damage results in less consistent body rhythms that are no longer synchronized to environmental patterns of light and dark

• The SCN generates circadian rhythms in a genetically controlled manner: cells extracted from the SCN & maintained in a tissue culture continue to produce action potentials in rhythmic patterns

Retinohypothalamic path

Light resets the SCN via a small branch of the optic nerve known as the retinohypothalamic path

• Travels directly from the retina to the SCN

• The retinohypothalamic path comes from a special population of ganglion cells that have their own photopigment called melanopsin

• The cells respond directly to light and do not require any input from rods or cone

How does the SCN regulate walking and sleeping

The SCN regulates waking and sleeping by controlling activity levels in other areas of the brain

• The SCN regulates the pineal gland, an endocrine gland located posterior to the thalamus which secretes melatonin, a hormone that increases sleepiness

How does melatonin work

• Melatonin secretion usually begins 2-3 hours before bedtime

• Melatonin feeds back to help reset the biological clock through its effects on receptors in the SCN

• Melatonin taken in the afternoon can phase-advance the internal clock and can be used as a sleep aid (a morning dose can phase-delay over time)

What’re the two types of genes that generate the circadian rhythm

• Two types of genes generate the circadian rhythm

  • Period: produce proteins called PER

  • Timeless: produce proteins called TIM

• PER and TIM proteins increase the activity of some neurons in the SCN that regulate sleep and waking

Sleep reduces____

• Adenosine

  • Decreasing sleep pressure, or process S(sleep drive)

Hypnogram

Hypnogram shows typical “sleep architecture” (stage -to -stage progression through stages of sleep for an 8 -hour evening; there is much variability from person to person)

Beta waves

beta waves are present when one is awake and focused

Alpha waves

Alpha waves are present when one enters a state of relaxation

Stage 1 of sleep

• The EEG is dominated by jagged, irregular, low-voltage waves

• Brain activity begins to decline; Stage 1 sometimes accompanied by dream-like hypnogogic sensations

Stage 2

• Sleep spindles: 12- to 14-Hz waves during a ½ second bursts

• K-complex: a sharp, high-amplitude negative wave followed by a smaller, slower positive wave

• associated w/ mem orginization, hormone regulation, synaptic plasticity, relaxation

Stage 3-4

Stages 3-4 constitute slow wave sleep (SWS), characterized by:

• EEG shows slow, large-amplitude delta waves

• Slowing of heart rate, breathing, and brain activity

• Highly synchronized neuronal activity

• Tissue repair, replenishing of immune system, growth processes, memory consolidation, flushing out metabolic byproducts (cleaning house)

Rapid eye movement sleep (REM)

• Rapid eye movement sleep (REM) are periods characterized by rapid eye movements during sleep

• EEG waves are irregular, low-voltage, and fast

• Postural muscles of the body are more relaxed than other stages

• REM associated w/ Learning & memory, enhanced creativity, improved mood, brain development; neurotransmitter synthesis & replacement

Summary, purpose of NREM stage 2 sleep

Sleep spindle “transfer” of new memories from temporary “flash drive” (hippocampus -based storage) to cortical-dependent long -term storage; consolidation of procedural motor memories

Summary, purpose of NREM stage 3-4 sleep

Replay and consolidation of long-term, explicit memories (selective synaptic strengthening and weakening of memories)

Summary, purpose of REM sleep

Memory consolidation & “integration” (restructuring, transformation, schematization) of new long -term explicit memories with older memories and general knowledge

At what time of the night does stage 3 (SWS) predominate

• early in the night

• SWS dec as the night goes on

At what time of the night does REM sleep predominate

• REM sleep predominates as the night goes on

• REM most strongly associated w/ dreaming, but people also report dreaming in other stages of sleep.

Brain function in REM sleep

During REM sleep

• Activity increases in the pons (which triggers the onset of REM sleep) and the limbic system (emotional systems), parietal cortex, and temporal cortex

• Activity decreases in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex

PGO waves

REM sleep is associated with PGO waves

• Waves of neural activity are detected first in the pons, then in the lateral geniculate nucleus of the thalamus, and then the occipital cortex

• REM deprivation results in high density of PGO waves during uninterrupted s

Sleep and college performance

• [W]e did not find that sleep duration the night before an exam was associated with better test performance. Instead we found that both longer sleep duration and better sleep quality over the full month before a midterm were more associated with better test performance” (p. 16).

• “Rather than the night before a quiz or exam, it may be more important to sleep well for the duration of the time when the topics tested were taught. The implications of these findings are that, at least in the context of an academic assessment, the role of sleep is crucial during the time the content itself is learned, and simply getting good sleep the night before may not be as helpful. The outcome that better ‘content-relevant sleep’ leads to improved performance is supported by previous controlled studies on the role of sleep in memory consolidation” (p. 16)

Sleep and College anxiety/Happiness

Sleep variability showed the opposite patterns with weekly happiness and weekly anxiety. End-of-semester happiness was associated with sleep variability

Baseline happiness predicted end-of-semester happiness. However, sleep variability also predicted end-of-semester happiness

Do dreams vary by culture?

yes

Why do we dream

• Freud

  • Guard sleep

  • serve as sources of wish fulfillment\

• Dream content

  • Varies by culture, gender anf age

  • Connects recent experiences

  • Manifest content vs latent content

Biological perspective on dreaming

• Biological research on dreaming is complicated by the fact that subjects often cannot accurately remember what was dreamt

• Two biological theories of dreaming include:

  • Activation-synthesis

  • Neurocognitive mode

Information-processing hypothesis for why we dream

To integrate new information with old information.

Activation-synthesis hypothesis for why we dream

Dreams begin with spontaneous activity in the pons, which activates parts of the cortex; the cortex synthesizes a “story” from the pattern of activation

Neurocognitive hypothesis for why we dream

Dreams are just “thinking” under “unusual conditions”

Evolutionary (and cognitive development) hypothesis for why dream

Dreams simulate reality, better preparing us for the waking world

The activation-synthesis hypothesis for why we dream

The activation-synthesis hypothesis suggests that dreams begin with spontaneous activity in the pons, which activates many parts of the cortex

• The cortex synthesizes a “story” from the pattern of activation

• Sensory information is sometimes integrated, but usually not

• When dreaming, you really can’t move, and this is also a common dream

What is the difference between the neurocognitive model and the activation synthesis hypothesis

The neurocognitive model is very similar to the activation-synthesis hypothesis, in that dreams begin with arousing stimuli generated within the brain, but suggests that dreams are similar to thinking (rather than random), just “thinking” under unusual circumstances.

Pontomesencephalon

The pontomesencephalon is a part of the midbrain that contributes to cortical arousal

• Axons extend to the hypothalamus, thalamus, & basal forebrain, which release acetylcholine & glutamate, and produce excitatory effects on widespread areas of the cortex\

• Stimulation of the pontomesencephalon awakens sleeping individuals and increases alertness in those already awake

Locus coeruleus

The locus coeruleus is a small structure in the pons whose axons release norepinephrine to arouse various areas of the cortex and increase wakefulness

Role of hypothalamus in wakefulness and arousal

The hypothalamus contains neurons that release histamine to produce widespread excitatory effects throughout the brain

Orexin

• Orexin is a peptide neurotransmitter released in a pathway from the lateral nucleus of the hypothalamus highly responsible for the ability to stay awake

• Stimulates acetylcholine-releasing cells in the basal forebrain to stimulate neurons responsible for wakefulness and arousal

• The basal forebrain is an area just anterior and dorsal to the hypothalamus

Hunger

It is a combination of learned and unlearned factors that contribute to hunger & eating behavior

• Biological influences

• Psychological influences

Digestion

The function of the digestive system is to break down food into smaller molecules for cell use

Short and long term regulation of feeding

• The brain regulates eating via messages from many sources: the mouth, stomach, intestines, fat cells, etc.

  • The desire to taste (and sensations like chewing) are motivating factors in hunger and satiety

what is one of the main signals to stop eating

• Distention of the stomach (stretching, expansion)

• The vagus nerve conveys information about the stretching of the stomach walls to the brain, while nerves from the duodenum convey information about the nutrient contents of the stomach

the duodenum

• The duodenum is part of the small intestine where initial absorption occurs (of significant amounts of nutrients)

  • Distention of the duodenum also produces feelings of satiet

• The duodenum releases CCK (cholecystokinin) in the presence of food which helps to regulate hunger by:

  • Closing the sphincter muscle between the stomach and duodenum, causing the stomach to hold its contents & thereby fill faster

  • Stimulating the vagus nerve to send a message to the hypothalamus that releases a chemical similar to CCK (a “fax” to the brain

_____, _____, and _____ levels also influence feelings of hunger

Glucose, insulin, and glucagon

How do most digested food enter the bloodstream

• Most digested food enters the bloodstream as glucose: an important source of energy for the body (nearly the only fuel used by the brain)

  • When glucose levels are high, liver cells convert some of the excess into glycogen and fat cells convert it into fat  When low, the liver uses glucagon to converts some of its glycogen back into glucose

insulin

• Insulin is a pancreatic hormone that enables glucose to enter the cell

  • Insulin levels rise as your get ready for a meal (in anticipation of additional glucose entering the blood) → higher insulin levels permit residual blood glucose to enter cells

  • Insulin levels continue to rise while we eat, but eventually, significantly high levels of insulin will decrease appetite

Glucagon

• Glucagon is a pancreatic hormone that stimulates the liver to convert some of its stored glycogen back into glucose (to replenish low supplies in the blood)

  • As insulin levels drop, glucose enters cells more slowly and hunger increase

Difference between Type 1 and Type 2 diabetes

• For people with Type 1 diabetes, insulin levels remain constantly low, but blood glucose levels are high

  • People eat more food than normal, but excrete the unused glucose and end up losing weight

• For people with Type 2 diabetes, insulin levels remain constantly high, but cells have become “insulin resistant” and so hunger remains high

Leptin

• Long-term hunger regulation is accomplished via the monitoring of fat supplies by the body

• The body’s fat cells produce the peptide leptin, which signals the brain to both increase and decrease eating:

  • Low levels of leptin increase hunger, while high levels of leptin decrease hunger and increase physical activity and immune system activity, but:

• Higher levels of leptin do not decrease hunger substantially…

  • Many obese individuals are less sensitive to leptin (despite high levels of leptin, they retain high levels of hunger)

  • Some people are obese because of a genetic inability to produce leptin (and for these people, taking leptin helps them to lose weight), but the incidence of this condition is low, so it can’t explain the obesity epidemic

Arcuate Nucleus

• Information from many parts of the body regarding hunger impinge on the arcuate nucleus (the “master area” for hunger)

• The arcuate nucleus is a part of the hypothalamus containing two sets of neurons:

  • Neurons sensitive to hunger signals

  • Neurons sensitive to satiety signals

What is the role of the Arcuate nucleus in the feeding circuit in the hypothalamus