SL - The brain and behaviour - NTs (ACh) and their (its) effect on memory Flashcards
Acetylcholine, physostigmine, and scopolamine.
Acetylcholine (ACh) -> a neurotransmitter that is associated with spatial memory and the consolidating and encoding of memory.
Physostigmine -> ACh agonist - excites cholinergic transmission.
Scopolamine -> ACh antagonist - inhibits cholinergic transmission.
Rogers and Kesner (2003)
ONLY USE FOR ANIMALS
Aim ->
To investigate the role of acetylcholine (ACh) during the
encoding and retrieval of spatial information.
Method ->
Rats had cannulae surgically placed in their brains to deliver chemicals to specific regions of the hippocampi and were tested for their ability to learn a simple maze. The rats ran the same maze in blocks of five, with two blocks run each day. Encoding was measured by comparing errors made in the first five trials of one day with the errors made in the final five trials of that same day. Retrieval was measured by comparing errors made in the final five trials of one day with the errors made in the first five trials of the next day.
There were three conditions: rats injected with physostigmine (ACh agonist - enhancing the transmission of acetylcholine), scopolamine (ACh antagonist - inhibits the transmission of ACH), and a saline solution (a control condition).
Results -> Scopolamine condition encoded worse but consolidated better. Physostigmine encoded better but retrieved worse. Results were in comparison to the control condition.
Conclusion -> ACh has two clear effects on memory processes: it facilitates the encoding of new information and inhibits the consolidation (long-term storage) of information. The reason for this two-fold function is to enable the efficient processing of information. One particular region of the hippocampi is involved in both the encoding and consolidation processes. These processes interfere with each other, and so for one to happen effectively the other must be inhibited. This is what ACh does.
Evaluation ->
✔ The measurements of encoding and retrieval were well-conceived and enabled a precise identification of the role of ACh in spatial memory.
✔ The use of rats enabled otherwise-unobtainable insights to be gained. Additionally, there has been research that has found rats’ brains are similar to ours so rat brains may be a suitable model for human brains.
❌ Cannot apply to human brains - Rat brains are not human brains so there remain questions over the usefulness of animal models for the understanding of human brains.
❌ Ethical issues ->The rats are likely to have suffered through the procedure for, and effect of, fixing cannulae in their brains. They were also killed at the end.
Gais and Born (2004)
Aim ->
To investigate the effect of acetylcholine on consolidation.
Method ->
All participants also received a placebo (saline solution). Some participants received an infusion of physostigmine, which stimulates acetylcholine production, over two hours. There were 4 conditions: sleep with physostigmine, sleep without physostigmine, awake with physostigmine, and awake without physostigmine. The experimental “sleep” group were awoken 3 hours after falling asleep and then all participants then completed word memory tests.
Results ->
During sleep, memory for the declarative wordlist task distinctly decreased after administration of physostigmine as compared with placebo. In the wake condition, the elevation of acetylcholine did not result in decreased memory performance but in an insignificant increase in wordlist recall as compared with that in the placebo condition.
Conclusion ->
Acquisition of declarative information (learning and memory for events) when we are awake needs higher acetylcholine levels. Although the difference in encoding was insignificant, Gais and Born suggested this could be because ACh was already present in the brain so using an agonist would not significantly affect the impact. However, the processing and storage of the materials require a period of low acetylcholine levels. So, high acetylcholine is needed for information to be retained in the hippocampus (encoding), and low acetylcholine is needed for that information to enter long-term memory (consolidation).
Evaluation ->
✔
✔
❌ Poor generalisability -> This was a small experiment (29 ppts) on males only and therefore has a gender bias. Also, there was a limited age range of the participants (between 18 and 35 years old). This means the results can only be applied to a very specific group.
❌ Ethical issues -> Protection from harm: as physostigmine can have unpleasant side-effects, there was a small risk of physical harm and mental stress being caused to participants.
Rasch, Gais and Born (2006)
Aim:
To see if lowering cholinergic neurotransmission after learning supports the consolidation of declarative memory.
Method ->
Eighteen male ppts took part in this repeated measures experiment, with two sessions that were two weeks apart. Each ppt experienced both conditions (one with an ACh antagonist, scopolamine, and one with a saline placebo).
Ppts were tested for encoding (learning a list of numbers followed immediately with a recognition task) and for consolidation (learning a list of word-pairs, memory for which was tested ten hours later).
Results ->
Encoding: Ppts performed significantly worse on this task when they had received the ACh antagonists.
Consolidation: Ppts performed significantly better on this task when they had received the ACh antagonists.
Conclusion ->
ACh supports encoding and inhibits consolidation.
Evaluation ->
✔ Repeated measures -> loss of participant variables.
✔ High validity -> lab - high control
❌ The ACh antagonists used would have had a global impact, and so the effects on memory might have been down to systems other than those that R, G & B suggested.
❌ Low generalizability -> small sample size - just eighteen ppts (or 36 as the design was repeated measures).
Agonist
Chemicals that imitate or enhance the effect of a NT.
Antagonist
Chemicals that block the effect of a NT. Not simply causing the opposite effect
