rodgers and kesner

NEUROTRANSMITTERS AND MEMORY ENCODING

Key Focus: Rogers & Kesner (2003)

KEY TERMS DEFINED

• Neurotransmitters: Chemical messengers that transmit signals across synapses between neurons. They influence behaviors such as learning, memory, and emotion.

• Acetylcholine (ACh): A neurotransmitter involved in memory formation and learning. It is highly concentrated in the hippocampus and plays a central role in encoding spatial memories and consolidating new information.

THEORY

• Acetylcholine facilitates the encoding of new memories by enhancing neural communication in the hippocampus.

• A decrease in acetylcholine levels (e.g., through the use of scopolamine) disrupts memory formation, particularly spatial memory encoding, but may not significantly affect retrieval of existing memories.

AIM To investigate the role of acetylcholine in the encoding and retrieval of spatial memory in rats.

METHOD

• Subjects: 30 rats were used and acclimated to a Hebb–Williams maze (a standardized spatial learning task).

• Rats were randomly allocated to one of two groups:
  

  • Group 1: Received scopolamine injections (acetylcholine inhibitor).

  • Group 2: Received saline solution (placebo).

• Injections were made directly into the hippocampus to isolate the effect of acetylcholine.

• Encoding was measured by comparing the number of errors made during the first five vs. last five trials on Day 1.

• Retrieval was assessed by comparing the first five trials on Day 2 to the last five trials on Day 1.

FINDINGS

• Rats injected with scopolamine made significantly more errors during encoding, showing impaired spatial memory formation.

• No significant differences in retrieval were found between groups, suggesting acetylcholine primarily affects encoding, not retrieval.

APPLICATION

• Highlights the biological role of neurotransmitters (specifically acetylcholine) in memory encoding.

• Supports drug development for memory disorders such as Alzheimer’s disease, which involve acetylcholine deficits.

• Contributes to the biological approach in cognitive psychology, showing how neurotransmitters affect cognitive processes like memory.

EVALUATION

Strengths

• Controlled experimental design: Use of a placebo helps control for the potential stress of injection, improving internal validity.

• Targeted manipulation: Injection directly into the hippocampus ensures that effects are specific to acetylcholine activity in the brain region relevant to memory.

• Establishes a clear cause-and-effect relationship between acetylcholine levels and memory encoding.

Limitations

• Reductionist: Focuses only on acetylcholine, ignoring the potential influence of other neurotransmitters like dopamine or glutamate in memory.

• Low generalizability: Animal models, while useful, cannot fully represent the complexity of human memory systems.

• Low ecological validity: The Hebb–Williams maze is an artificial task that doesn’t fully mimic real-world memory challenges or environments.

ETHICAL CONSIDERATIONS

• The procedure involved injections into the hippocampus, which may have caused stress, discomfort, or harm to the animals.

• However, the study followed animal research guidelines, and the use of animals is justified by the potential human benefit of understanding memory mechanisms.

UNANSWERED QUESTIONS

• Would these findings generalize to humans?

• Would a similar design using non-invasive neuroimaging in humans replicate the findings?

• Are there long-term effects of scopolamine on memory function?

CONCLUSION

• Rogers & Kesner (2003) provides clear experimental evidence that acetylcholine is essential for encoding spatial memory, but does not significantly impact memory retrieval.

• It supports the biological basis of memory, consistent with findings from human studies like Antonova et al. (2011), and adds to the understanding of neurotransmitter-specific roles in cognitive processes.