Time Flashcards
Humans are sensitive to the day/night time and 24-hour cycle. Name an example:
waking up just before your alarm goes off and not just because of the sun:
jetlag
Name an example of Period Timing:
Circadian rhythms.
Question: is the cyclical behaviour really controlled by time per
se? Or is it controlled by stimuli that are always present at that
particular time?
Wheel running in the rat (described in Carlson):
What is the term used to describe learning to respond at a particular time of day?
Period Timing
How does a stimulus cue of light on and light off periods affect rats exercise activity?
Rats increased their exercise activity between the light off periods (nocturnal) even when the timings of the light off were shifted from 8am-8pm to 4pm and midnight.
What is the term used to describe learning to respond after a particular interval of time?
Interval Timing
Stimuli of light acts as a ? synchronising the internal clock.
Zeitgeber
(Roberts, 1965). found Cockroaches increased activity at which time of day when removing visual cues cycle that drifted until increased activity started?
Dusk
15 hours before dusk (cycle slightly less than 24 hours).
This is evidence for some sort of intrinsic clock in animals’ heads
(but not that accurate) Without the light stimuli, time drifts.
Restoring visual cues produced a gradual shift back to correct
time.
Is the apparent internal 24-hour clock the result of environmental experience or is it innate?
Bolles & Stokes (1965) studied rats who were born and reared under either 19, 24 or 29-hour light/dark cycles. Then fed at a regular point in their own particular cycle and food delivery is signaled a few hours before by a change in lighting.
Change in lighting before food was given.
What were the findings?
Rats on the 24-hour cycle learned to anticipate food
But rats that were trained on the 19 or 29-hour light/dark cycles didn’t:
Showing no anticipatory response of food, even becoming less active
Conclusion:
Not the product of experience, suggests innate
What happens when rats are presented with constant dim light when no light cues are available? Will their rates of exercise change?
Findings suggest 24-hour clock activity:
They maintained their exercising behaviour on an approximately
25-hour cycle
The exercise got a little later each day (active period was drifting)
Evidence for a physiological system that could provide this 24-hour clock:
Which brain structure is thought to be involved in animals’ 24-hour clock cycle?
The suprachiasmatic nucleus (SCN) of the hypothalamus.
The metabolic rate in the SCN varies as a function of the day-night cycle.
Lesions (damage) of the SCN:
Abolish the Circadian Regularity of foraging and sleeping in the rat. Receives direct and indirect inputs from the visual system, which could keep circadian rhythms entrained with the real day-night cycle.
Disruption in circadian rhythms can be responsible for physical illness Who is more susceptible to heart disease, diabetes, infections and even cancer?
shift workers
Which type of timing to rats do during conditioning?
Interval Timing
eg. pairing tone (20sec) and food
but instead of looking at responding for the entire duration of the tone, you look to see how it is distributed during the timing intervals
Results: rats response to the food coming gets stronger as the tone intervals proceed
If tone stimulus keeps going, animals will show a peak of expectation, then lose interest and stop responding
Conclusions:
shows that they know at what time period after the tone the food will come
More recent work suggests every cell in the body has a circadian rhythm, which are all under the control of which brain region?
This can dictate e.g. circadian variation in
sensitivity of tumours to chemotherapy.
the SCN.
“Chronotherapy enjoyed a publicity boost.. the Nobel Prize in Physiology or Medicinewas awarded to a trio of scientistsfor elucidating the cellular mechanisms that control circadian rhythms. The circadian clock is a remarkable system. A central timekeeper in the hypothalamus orchestrates a network of peripheral clocks in nearly every organ and tissue of the body,turning on and off a bevy of genes, including some that encode the molecular targets for drugs and the enzymes that break drugs down. These clock genes are particularly important in cancer because they govern cell cycles, cell proliferation, cell death and DNA damage repair — all processes that can go haywire in cancer.”
In Alzheimer’s disease the phenomenon of sundowning refers to:
The worsening of symptoms in afternoon/evening
Church & Gibbon, 1982:
Rats in lit chamber. Occasionally houselight went off, for a 0.8, 4.0
or 7.2 sec (the CS). When the lights went on again a lever was
presented for five seconds. If the rat pressed the lever after a
4-sec CS it got food, otherwise it did not. Then tested with a
range of stimulus durations (0.8 - 7.2 secs).
After how many seconds were the rats most likely to make a response?
Rats were more likely to make a response after 4 seconds of darkness(where food is rewarded)
compared to shorter/ longer periods of darkness
Church & Gibbon, 1982:
Rats in lit chamber. Occasionally houselight went off, for a 0.8, 4.0
or 7.2 sec (the CS). When the lights went on again a lever was
presented for five seconds. If the rat pressed the lever after a
4-sec CS it got food, otherwise it did not. Then tested with a
range of stimulus durations of 2, 4, 8 seconds.
What did What is Weber’s Law show?
reaches half maximum at
~ 50% of duration in each case
Responding rate drops by half when stimulus duration is dropped by half
What is Weber’s Law: Scalar property of timing?
SCALAR TIMING THEORY
Gibbon, Church & Meck, (1984)
Fill in this model which predicts performance:
SCALAR TIMING THEORY
Gibbon, Church & Meck, (1984)
Explain this model which predicts performance:
During the SCALAR TIMING THEORY, stored value used in reference memory to decide whether or not to respond on the next trial.
On each trial the animal compares the number of pulses in working memory (N * t) with a random value drawn from those stored in reference memory Nmx.
Which component is key for this process?
If the values are close, then the animal responds.
What is going on here?
The animal uses ONE of the values in reference memory to decide when to respond.
Smaller numbers closer together = now its time to respond
