NonCircadian Rhythms

Question 1

Ultradian vs Circadian vs Infradian

Answer 1

Ultradian: Signalling, work, info transfer (Seconds to hours)

Circadian: Anticipation of demand (Day)

Infradian: Developmental changes (Weeks to years)

Question 2

Example of ultradian rhythm - Heartbeat
Is it a clock or pacemaker?

Answer 2

Pacemaker
- Can continue beating w/out purpose in its rate
- Just a cycle that returns to beginning and triggers itself

Question 3

Episodic ultradian event example: hormone release
- What does “episodic mean”
- How is the rhythm like?
- How does it communicate?

Answer 3

Episodic:
- Pulses happen in an interval of about 1 day
- Pulses can happen randomly (unstable/in random episodes)

Not very stable rhythm (unstable oscillator or nothing producing oscillation)
- Periods change over time

Communicates in pulsatile fashion
- May need more than one pulse to get chemical reactions started

Question 4

Episodic ultradian events
Basic rest-activity cycle

Answer 4

Episodic ultradian events:
- Rhythms not directly related to environmental cycle
- Oscillators or have an oscillator

Basic rest-activity cycle:
- Activity goes for certain time until worn out, before repeating
- No timer of how long intervals need to be

Question 5

In the basic rest-activity cycle, why are factors like food, activity, body temp, brain temp, and BAT temp all spiking at the same time?

Answer 5

All parts of the organism are working together during food/activity
- Causes the rhythm (spikes) to appear

Question 6

Mouse running wheel activity w/ faulty SCN and amphetamine in drinking water (constant light)

Answer 6

1) Mix of short and very long periods (SCN either broken into pieces or no longer strong enough to keep rhythm)

2) Amphetamine put in drinking water, causing short period to emerge
- Dopamine gets brain aroused -> activity burst
- But more activity gets it to be tired faster (short period eventually disappears)

3) Long period from amphetamine appears
- Methamphetamine induced oscillators (or dopamine regulated circadian oscillator)

4) Spontaneous rhythm occurs
- Most likely caused by small circadian system that failed in beginning

Question 7

Mouse placed in constant light, no amphetamine but given daily food
- Is there a basal rest-activity cycle?

Answer 7

SCN followed light (causing long periods) but shell part not receiving light continues as if in dark (causing short periods)

There is a BRAC happening:
- Mouse shows activity before giving food (not just random hours of onset everyday)

Question 8

True or false
Ultradian system can he controlled by the dopamine system too, not just SCN

Answer 8

True

Question 9

Locomotion is inhibited and controlled by the firing of?
They couple locomotion speed to what?
How is CA1 activity increased?
How do carrier theta/beta waves communicate to tissues?

Answer 9

Medial septal VGluT2 neurons
Theta oscillations and CA1 activity
Speed-dependent disinhibition of CA3 and EC input
At specific areas of wave, tissues will be triggered (keeps a sequence that causes rhythm)

Question 10

True or false
Clocks experience increasing astronomical time?

What are interval timers?

Answer 10

False - Cosmological time

Interval timers: Mechanism for measuring duration (time until and time since condition)
- Brain remembers number of cycles / fractions of cosmological time

Question 11

Scalar expectancy theory
Beat frequency model

Answer 11

SET: Time perception is on a continuum w/ units of equal magnitude
- Pacemaker: Generates pulses at constant rate
- Switch: Threshold mechanism that allows pulses to accumulate in memory when interval is being timed
- Accumulator: Sums accumulated pulses and estimates duration of interval
- Attention can impact how many beats are recorded

BFM: Diff between two diff beat freqs (beat produced when 2+ diff freqs presented, interference causes beats)
- Neurons can detect beat freq and fire in sync to create rhythm

Question 12

Effect of methamphetamine on response latency

Answer 12

Increases latency, but error doesn’t change

Question 13

An internal clock model requires what 3 primary stages/components?

Answer 13

1) Internal clock processes
- Clock substrate and readout mechanisms

2) Reference memory for duration
- Long-term store of clock values at time of reinforcement

3) Comparison mechanism
- Evaluates similarity between clock values and duration memories

Question 14

How do you make judgments about:
- How fast time is passing
- How much time has passed
- How much time is left to go

Answer 14

Feeling, current sense of time (depends on attention of beats)

Requires memory of start and accumulation of interval length

2 + initial sense of task duration

Question 15

What part of the brain is most active when paying attention to beats?

Answer 15

Midfrontal cortex

Question 16

Aged hamsters vs healthy hamsters on running wheel

Place preference memory in hamsters (fragmented vs consolidated)

Rats’ spatial memory (morris water maze) w/ non-shifted vs shifted (light advances 3 hours per day)

Answer 16

1) Aged hamsters have more scattered/fragmented rhythms

2) Hamsters put in one box w/ wheel (paired) and another box w/out wheel (unpaired)
- Fragmented group shows equal playing in both boxes while consolidated group shows more playing in paired box

3) Shifted rats learn as well as non-shifted
- But shifted fail to retain what they learn and spend equal time in quadrants during testing

Question 17

Time memory
Why is this important?

Answer 17

Time memory: Learning and remembering time of day
- Animals need to remember when they come across predators at locations

Question 18

Explicit time memory vs Implicit time memory

Answer 18

Explicit: Time of day is discriminative cue and part of context that must be learned
- Ex: Time-place learning, food entrainment

Implicit: Time of day is not a discriminative cue and memory is implied by the response of subject
- Ex: Time memory

Question 19

Explicit time memory experiment: Rats and electrifiable grid

Implicit time memory experiment:
1) Rats and post-training context preference (for running wheel)
- CT 13 and CT 04
2) Conditioned place avoidance

Answer 19

Explicit:
- Electrifiable grid near food that turns on at certain times of day
- Rats eventually learn which ones are safe at which times of day

Implicit:
- Rats register time of day that significant conditions occur; recurrence of condition at same time on following days
- Rats conditioned at CT13 prefer running at CT13 than CT04
- Rats conditioned at CT04 prefer running at CT04

• 2 chambers: safe and shock, which turns on every 24 hours
• Rat shows more preference for safe chamber every 24 hours

Question 20

True or false
The suprachiasmatic nucleus (SCN) is required for time memory

Explain the results of the experiment that show this

Answer 20

False - Not required

Both intact and SCN lesioned animals show passive avoidance at same 4-hour interval every 24 hours

Question 21

Experiment:
Preference for unpaired safe context when trained at ZT11 vs ZT03
(ZT11 is eight before night activity, ZT03 is in the middle of day)

Answer 21

Originally had preference for safe context at ZT11 and ZT03 w/ respective training
- 18 days after conditioning, even when trained at ZT03, showed more preference at ZT11
- Only happens if there’s no further reinforcement

Question 22

Experiment: Conditioned passive avoidance in tau mutant hamster (20-hr period) w/ SCN intact and lesioned

Answer 22

Intact:
- Preference every 20 hours and 24 hours

Lesioned:
- Preference only at 24 hour intervals (no more 20 hours)
- Shows that there’s a cycle going on at 24 hours that doesn’t rely on SCN

Question 23

True or false:
Entrainable oscillator underlying time memory can be set to any phase of the SCN clock

SCN is required for time memory and cannot be a Zeitgeber

A pre-existing memory can be reset to another time

The oscillator is not affected by altered clock genes and isn’t classically conditioned

Answer 23

True

False
- SCN isn’t required and can be Zeitgeber

True

True

Question 24

Experiment showing time memory is dopamine dependent:
ZT11 vs ZT03
AMPH (dopamine agonist) vs Haloperidol (dopamine antagonist)

Answer 24

Rat given AMPH injection at ZT11 only
- Shows preference for location where it got injection at ZT11 but not ZT03

Rat given haloperidol injection at ZT11 only
- Shows preference for other location at ZT11 but not at ZT03

Question 25

Experiment showing how time memory can be reset using amphetamine
(Safe vs shock)

Answer 25

Saline group:
- Rat showed more preference for safe chamber after 48 hours

AMPH group:
- Rats failed to show preference after 48 hours; showed at 64 hours instead
- AMPH caused cycle to be longer