Two Key Studies of the Brain & Behaviour: Animals (HL IB Psychology)

Key Study One: Rosenzweig et al. (1972)

Note: You learned about neuroplasticity in the SL Biological Approach (see the RNs on this site which cover the topic) using research by Maguire et al. (2000) and Luby et al. (2013) which both investigate neuroplasticity in humans. This key study looks at neuroplasticity in rats’ brains so make sure that you DON’T use it when answering a question on neuroplasticity in relation to human behaviour i.e. only use this research for a HL Extension question on Paper 1 Section B.

Aim: To investigate neuroplasticity in rats’ brains when they are exposed to either a highly enriched environment or an impoverished environment.

Procedure: Three male rats were chosen from 3 separate litters. They were then randomly assigned to one of three conditions. One rat remained in the laboratory cage with the rest of the rats; another was assigned to the "enriched" environment cage; and the third was assigned to the "impoverished" cage. There were 12 rats in each of these conditions for each of the 16 experiments.

The three different environments were:

1.   The standard laboratory cage - several rats in an adequate space with food and water available 

2.   The impoverished environment - a slightly smaller cage isolated in a separate room in which the rat was placed alone with adequate food and water

3.   The enriched environment – six to eight rats in a large cage furnished with a variety of objects with which they could play and exercise on

The rats lived in these different environments for periods of four to 10 weeks. After this phase of the procedure they were humanely sacrificed so that brain autopsies could be conducted to investigate differences in the brains of the rats across the conditions.

Results: 

• The cerebral cortex (the part of the brain that responds to experience and is responsible for movement, memory, learning, and all sensory input) of the rats who had lived in the enriched environment were significantly heavier and thicker than the rats who had lived in the impoverished environment 

• There were no significant differences between the rats in terms of the number of neurons per brain but the enriched environment rats had larger neurons than the impoverished environment rats

• An electron microscope showed that the synapses of the enriched rats' brains were 50% larger than those of the impoverished rats

Conclusion: Living in an enriched environment may significantly increase the cerebral cortex of rats’ brains compared to rats who live in an impoverished environment.

Evaluation of Rosenzweig et al. (1972)

 Strengths

• The use of a standardised procedure and clinical methodology to study the rats’ brains means that this study has good reliability

• The findings of this study have some application to therapeutic settings e.g. with dementia patients (providing stimulation may help to offset or prevent further loss of brain function)

 Limitations

• It is difficult to generalise the findings as rats’ brains are simplistic compared to human brains, so some caution is necessary when considering the results

• There are ethical concerns not only due to the fact that the animals were destroyed after the procedure, but the use of the impoverished environment may have caused some deterioration in the rats who were exposed to such a negative environment

Key terms: Cerebral cortex Enriched environment Impoverished environment

An enriched environment compared to an impoverished environment

Key Study Two: Fadda et al. (1996)

Note: You learned about neurotransmitters in the SL Biological Approach (see the RNs on this site which cover the topic) using research by Fisher et al. (2005) and Brunner et al. (1993) which both investigate neurotransmitters in humans. This key study looks at neurotransmitters in rats’ brains so make sure that you DON’T use it when answering a question on neuroplasticity i.e. only use this research for a HL Extension question on Paper 1 Section B.

Aim: To examine whether rats’ performance in a T‐maze was associated with increased acetylcholine (ACh, a neurotransmitter associated with memory and learning) in the hippocampus.

Procedure: 

• A group of rats selected to be in the experimental condition were deprived of food for 23 hours to make them hungry and at 80% of their body weight

• The rats were then trained using a T‐maze (a maze in the shape of a ‘T’) on 12 consecutive trials (one trial = one session) in which they had to alternate between the right and left arms of the maze to find a sunflower seed 

• On the first trial of each session, access to one of the arms was blocked, forcing the rat to enter only the opposite arm 

• On each of the next 11 trials the food was placed in the arm opposite to that in the previous trial and both arms were unblocked (free‐choice trials) 

• A correct trial ended with the rat eating the food; an incorrect trial ended with the rat reaching the empty food cup

• Rats in the control group were introduced into the T‐maze only on the day of the experiment but were handled in the same way and for the same length of time as the trained rats were

• Acetylcholine in the rats’ brains was measured by use of a specially implanted probe.

Results: 

• There was an increase in ACh in the hippocampi of the trained rats before the task, but not in the control rats 

• This finding shows that ACh increases with anticipation of a learning task 

• There was an increase in ACh in the hippocampi of the control group rats during the first ten minutes of the task, after which the ACh decreased back to the basal level and stayed there 

• The ACh stayed high throughout the task for the trained rats and decreased slowly after the task

 Conclusion: ACh may play a key role in rats’  learning and memory.

Evaluation of Fadda et al. (1996)

 Strengths:

• The control group rats were handled in the same way and for the same time as the trained rats prior to the experiment which should eliminate any bias in the treatment of the rats which increases the internal validity of the study

• Rats are highly sensitive, intelligent creatures which means that they are good subjects to use in research on learning such as this one

 Limitations

• Using lab rats who live in captivity lacks ecological validity as this is not how rats use memory or learning in the real world

• The study does not mention if the control group rats similarly had their food intake reduced for the period before the test

Key terms: Acetylcholine T-maze Hippocampus

ACh appeared to have a positive effect on rats’ brains