BLA: Martinez and Kesner (1991)

Martinez and Kesner, 1991

On Acetylcholine and its Role on Memory Formation

Before reading, you should be comfortable with:
- neurotransmitters
- the principles of the biological level of analysis
- experimental methods used in the biological level of analysis

What is this study about?
This study was performed in the biological perspective, where lab rats were used to test the role that a neurotransmitter has in the formation of memory.

Aim?
To see the role that acetylcholine has on memory formation.

How was this "formation of memory" tested with lab rats?
The lab rats were put under three different controls:
1. Rats were injected with scopolamine (drug), which is known to block acetylcholine receptor proteins on the post-synaptic neurones. This means that acetylcholine, a hormone expected to help form memories cannot travel from one neuron to another, i.e. no nerve impulse is sent across neurones.
2. Rats were injected with physostigmine, a drug that is antagonistic towards acetylcholinesterase. Cholinesterase (or acetylcholinesterase) is what cleans up the acetylcholine from receptor proteins on the post-synaptic neurones, returning the neurones to their "resting potential", where no nerve impulse is being sent. Physostigmine blocks cholinesterase which prevents this "cleaning-up" of acetylcholine.
3. Rats were not injected or altered in any form at all.

Design: 
- Laboratory experiment
- Controlled variables (i.e. 3 conditions of the rats, drug amount, maze complexity)

Procedure:
1. All rats were placed in the maze individually and completed the maze (maze had reward of food at the end)
2. Rats were given their respective treatments (see 3 groups above)
3. Rats were placed in maze individually and time taken to complete maze was measured

Results?
- Condition 1 (rats that were injected with scopolamine) took the longest to complete the maze
- Condition 2 (rats that were injected with physostigmine) took the shorted amount of time to complete the maze
- Condition 3 (rats with no treatment) had maze-completion times between the condition 1 and condition 2 rats 

Interpretation?
- Scopolamine has the effect of preventing or slowing down the process of memory formation. This can be concluded because the rats given scopolamine took the longest to complete their mazes. Acetylcholine is involved in memory formation because scopolamine is what blocks acetylcholine receptors.
- Acetylcholine is involved in memory formation because the condition 2 rats were quickest in completing the maze: their injection of physostigmine prevented the removal of acetylcholine from the receptor proteins of the post-synaptic neurones.
- The more acetylcholine is available, the more productive memory formation is. This can be concluded because condition 3 rats were in-between the other two conditions in terms of maze-completion time.

Advantages of this experiment?
- The experimental method of this experiment makes it clear to see the cause-effect chain between the neurotransmitter acetylcholine and memory formation.
- Conclusions drawn from this experiment are therefore accurate.
- Multiple trials could have been easily performed
- Easily replicable
- Possiblity that humans can be treated with acetylcholine or physostigmine for memory-loss
- No differences in the role of acetylcholine between cultures (as rats were used, not people); results may be relevant for every human
- No people were harmed in this experiment
- No deception was used in this experiment

Disadvantages of this experiment?
- Rats were harmed
- Ethical concerns to the extent that the rats suffered
- The results cannot be completely applied to humans