C82LEA Biology of learning and memory

C82LEA Biology of learning and memory Learning about time Charlotte Bonardi

We are pretty good at estimating time periods, and making judgements about whether intervals are shorter or longer than each other. We are also sensitive to the day/night time cycle: jetlag (timing obviously not just to do with the sun) waking up just before your alarm goes off

We are pretty good at estimating time periods, and making judgements about whether intervals are shorter or longer than each other. We are also sensitive to the day/night time cycle: jetlag (timing obviously not just to do with the sun) waking up just before your alarm goes off How do we do it? Can animals do these things? How do they do it?

Distinguish periodic (learning to respond at a particular time of day) and interval timing (learning to respond after a particular interval of time).

Distinguish periodic (learning to respond at a particular time of day) and interval timing (learning to respond after a particular interval of time). PERIODIC TIMING e.g. 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):

4am 8am Midday 4pm 8pm Midnight ACTIVITY Light off Light on

4am 8am Midday 4pm 8pm Midnight ACTIVITY Light off Light on ACTIVITY Light off Light on

4am 8am Midday 4pm 8pm Midnight Constant dim light When no light cues are available they maintain behaviour on an approximately 25-hour cycle

Cockroaches (Roberts, 1965). Increased activity at dusk. When removed visual cues cycle drifted until increased activity started 15 hours before dusk (cycle slightly less than 24 hours). Restoring visual cues produced a gradual shift back to correct time. Entrainment : light acts as a zeitgeber synchronising the internal clock.

Cockroaches (Roberts, 1965). Increased activity at dusk. When removed visual cues cycle drifted until increased activity started 15 hours before dusk (cycle slightly less than 24 hours). Restoring visual cues produced a gradual shift back to correct time. Entrainment : light acts as a zeitgeber synchronising the internal clock Question: Is the apparent internal 24-hour clock the result of environmental experience?

Cockroaches (Roberts, 1965). Increased activity at dusk. When removed visual cues cycle drifted until increased activity started 15 hours before dusk (cycle slightly less than 24 hours). Restoring visual cues produced a gradual shift back to correct time. Entrainment : light acts as a zeitgeber synchronising the internal clock Question: Is the apparent internal 24-hour clock the result of environmental experience? Bolles & Stokes (1965) Subjects born and reared under either 19, 24 or 29 hour light/dark cycles. Then fed at a regular point in their own particular cycle....

animals on the 24-hour cycle learned to anticipate food.... Light change 29 22 15 8 1

but the others didn’t.... Light change 29 22 15 8 1

Light change 29 22 15 8 1

Is there any evidence for a physiological system that could provide this 24-hour clock? The suprachiasmatic nucleus (SCN) of the hypothalamus may be a candidate. The metabolic rate in the SCN appears to vary as a function of the day-night cycle. Lesions of the SCN will abolish the circadian regularity of foraging and sleeping in the rat. It also receives direct and indirect inputs from the visual system, which could keep circadian rhythms entrained with the real day-night cycle.

INTERVAL TIMING Consider a normal classical conditioning procedure: Tone (20 sec) --> food ? ? ?

.....so what happens if the stimulus keeps on going (and you omit the food)? The peak procedure

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).

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). 0.8 Response probability 0.4 0 2 4 6 8

0.8 0.4 0 2 4 6 8 Food after 2 seconds

0.8 0.4 0 2 4 6 8 Food after 2 seconds 0.8 Food after 4 seconds 0.4 0 2 4 6 8

0.8 Food after 2 seconds 0.4 0 2 4 6 8 0.8 Food after 4 seconds 0.4 0.8 0 2 4 6 8 0.4 Food after 8 seconds 0 2 4 6 8

Weber’s Law The generalisation that the just noticeable difference is proportional to the magnitude of the stimulus. Hence small amounts judged more accurately than large amounts

Weber’s Law The generalisation that the just noticeable difference is proportional to the magnitude of the stimulus. Hence small amounts judged more accurately than large amounts One versus two

Weber’s Law one versus two – absolute difference of one - difference as % of whole 0.5 One versus two

Weber’s Law 19 versus 20 – absolute difference of one - difference as % of whole 0.05 Nineteen versus twenty

Weber’s Law for comparable difficulty to the one versus two comparison you need to compare 20 versus 10... ten versus twenty

Weber’s Law This may be called the scalar property of timing (it applies to other judgements too). I / I = k I = Just discriminable change in intensity I = original intensity k = constant

One versus two Difference = 2-1 = 1 Ratio = (2-1)/2 = 0.5

One versus two Difference = 2-1 = 1 Ratio = (2-1)/2 = 0.5 Nineteen versus twenty Difference = 20-19 = 1 Ratio = (20-19)/20 = 0.05

Working memory N * t Reference memory K * N * t pacemaker t pulses per second comparator Scalar timing theory e.g. Gibbon, Church & Meck, (1984) response?

Working memory N * t Reference memory K * N * t pacemaker t pulses per second Pacemaker emits pulses at a constant rate t(although there may be some random variation). comparator response?

Working memory N * t Reference memory K * N * t pacemaker t pulses per second Pacemaker emits pulses at a constant rate t(although there may be some random variation). When a stimulus is presented, a switch is operated, and the pulses are allowed to accumulate in working memory. This will equal t multiplied by the number of seconds that have passed (N). comparator response?

Process 1: Storing duration of a stimulus in Short term memory

t = 1 per second(ish) Working memory N * t Reference memory K * N * t pacemaker t pulses per second 1 comparator 5-second stimulus: successive pulses stored in working memory response?

Process 2: Storing duration of a stimulus in Reference memory

Working memory N * t Reference memory K * N * t pacemaker t pulses per second 5 5.1 When the reinforcement occurs, pulses stop accumulating; the number of pulses in working memory (N * t) is now stored in reference memory comparator response?

Working memory N * t Reference memory K * N * t pacemaker t pulses per second 5.1 When the reinforcement occurs, pulses stop accumulating; the number of pulses in working memory (N * t) is now stored in reference memory; this storage is not always completely accurate -- there is some memory distortion. This is represented by K, a number that is close to 1.If K=1 then the memory is accurate; if K<1 then a smaller number of pulses is stored; if K>1 then a greater number is stored. comparator response?

Working memory N * t Reference memory K * N * t pacemaker t pulses per second 5.1 After several trials there will be several numbers stored in reference memory Nm1, Nm2, Nm3, etc -- each equal to the K * N * t for that particular trial. comparator response?

Working memory N * t Reference memory K * N * t pacemaker t pulses per second 5.1 4.7 After several trials there will be several numbers stored in reference memory Nm1, Nm2, Nm3, etc -- each equal to the K * N * t for that particular trial. comparator response?

Working memory N * t Reference memory K * N * t pacemaker t pulses per second 5.1 4.7 4.9 After several trials there will be several numbers stored in reference memory Nm1, Nm2, Nm3, etc -- each equal to the K * N * t for that particular trial. comparator response?

Working memory N * t Reference memory K * N * t pacemaker t pulses per second 5.1 4.7 4.9 5.0 After several trials there will be several numbers stored in reference memory Nm1, Nm2, Nm3, etc -- each equal to the K * N * t for that particular trial. Remember the error on each trial will not be the same comparator response?

Process 3: Using stored value in reference memory to decide whether or not to respond on the next trial

C82LEA Biology of learning and memory