Biopsychology of Motivation Flashcards
Richtor (1992)
hypothesized that animals have an internal mechanism that spontaneously generates this rhythm (biological clock)
Edogenous Circadian Rhythms
internally controlled cycles that last about a day
e.g. birds that migrate
how do we know that the rhythm we have is internally generated?
- If you stay up all night, you feel sleepier as it gets later, but then perk up a bit in the morning
- Animals kept in total darkness still keep to a 24 hour cycle (approx.) DeCoursey 1960 – rhythm of activity stays the same
- Humans kept in an environment with a 28hr cycle cannot synchronise, they slip back into a 24 hour cycle
- Blind and deaf animals generate nearly normal circadian rhythms
DeCoursey (1960)
Animals kept in total darkness still keep to a 24 hour cycle (approx.)
Richter (1967)
- theorized that we all have a biological clock = a mechanism in or brain that generates this cycle – physical part of our brain that keeps the time
- seems to be robust - maintained despite brain damage
Where is the biological clock?
Supachiasmatic nucleus above the optic chiasm
What happens to the SNL when damaged?
Damage to circadian rhythms
How do we know that the biologic al clock generates this rhythm automatically?
- Earnest et al 1979 - Remove the SCN and keep it is a tissue sulture it continues to procedure a 24 hour rhythm of action potentials
- Hamsters with a mutant gene coding a 20hr rhythm, SCN removed and implanted in normal hamsters, they start to live a 20hr cycle – good evidence that this part of the brain does all of the work in terms of our biological clock
How does the biological clock work?
- Regulates waking and sleeping through activity in the brain
- Controls the pineal gland = an endocrine (hormone) gland posterior (behind) the thalamus
- Releases melatonin – hormone that makes us sleepy
- SCN tells the pineal gland to secrete this hormone in the 24 hours so you are asleep in the night and awake in the day
Can the biological clock respond to the environment?
YES
Zeitgeber
‘time giver’
- anything that has an influence on the biological clock e.g. light, excersie
- most dominant Zeitmesser for land mammals is light
- But we also respond to exercise, noise, temperature and meals
- some marine animals respond to tides
- those in Scandinavian countries are insomniac because of 2 hours of daylight
- Hamsters living in constant light, SCN in one hemisphere out of phase with right
• No coordination!
• Two sleep and two wake cycles!
Jet lag
- Disrupting rhythms by crossing times zones
- Mismatch between biological clock and external stimuli
- not used to adapting to things so fast
- can be stressful and raise cortisol levels
Phase Delay
- travelling east to west (UK to USA)
- easiest to adapt to as you just
Phase Advance
- Travelling west to east (USA to UK)
- harder to adapt to as your nights are shortened
Those who work night shifts..
- Feel fatigued
- Cant sleep well during the day
- Don’t adjust when working at night, as the light levels aren’t high enough in artificial conditions
- Need to have a complete reversal to fully change the biological clock
Optic chiasm
- sits nect to the supachiasmatic nucleus
- where information is transferred from our retina, links and nerves to the eye
- important in light
Melanopsis
- special photopigment that knows light from dark
- responds directly to light
- repsonds slowly and turns off slowly
- So the SCN gets an idea of general light intensity – perfect to gauge time of day
Kalat - blind mole rat
blind mole rat can respond to light through melanopsin (can tell light from dark)
- other reptiles have third eye on their head where melanopsin is kept
EEG
can be used to detect electrical signals of spontaneous brain activity OR in response to a stimulus (ERP – Event Related Potential)
Stage 1 and 2 of sleep
irregular activity, high but declining, bursts of activity in stage 2, cortex still receiving sensory input e.g. can still wake up when someone touches you
Stages 3 and 4 of sleep
slow wave sleep (SWS) = neuronal activity is highly synchronized, sensory input reduced – harder to wake up
REM
- Also called paradoxical sleep because it doesn’t catagorise into the stages
- Neither nor deep sleep
- Can be categorized as Light because lots of brain activity
- But can also be catagorized as Deep because muscles are relaxed
What does the brain do during REM?
- Lateral geniculate neucleus in the thalamus (limbic system) → responsible for emotion
- Pons (brainstem) = ‘bridge’ axons from cortex cross here to spinal cord → movement (inhibits) – any signals going through movement or muscles go through this brain stem - it is not activated in a way that increases movement it actually inhibits, so your pons are activated and your muscles are relaxed as a result of this
- PGO waves (pons-geniculate-occipital) – work in a cycle – activity of pons so the muscles are relaxed, which leads to activity of the geniculate so you get lots of emotional activity and then lastly there’s the activity of the occipital cortex which is where a lot of visual processing occurs which is why we appear to see our dreams, feels like we are there, this is why we get rapid eye movement – controls our wakefulness
