Overview and Reflection on Brain changes in response to experience. Rachel Almeida

Transcription

1 Running head: Overview and Reflection on Brain changes in response to experience 1 Overview and Reflection on Brain changes in response to experience Rachel Almeida

2 Overview and Reflection on Brain changes in response to Experience 2 Abstract This paper explores the famed studies published by Mark R. Rosenzweig, Edward L. Bennett, Marian C. Diamond, and David Krech. This classic study, from the field of biopsychology, explored how environmental conditions affect the physiology of the brain. In this study, Brain Changes in Response to Experience, psychologists altered different environmental conditions in which they placed rats to live in over a selected period of time. After the allotted time had passed in the different living conditions, thorough research was then performed, examining different parts of the rats brains. Disclosed in this paper are the predictions, methods, procedures, and results of this classic study. Also included is the undoubtedly major contribution to the field of psychology which came as an unexpected, yet obvious result. Overview and Reflection on Brain changes in response to environment

3 Overview and Reflection on Brain changes in response to Experience 3 In 1960 psychologists Mark R. Rosenzweig, Edward L. Bennett, and David Krech published their first study on the effects of environmental complexity on brain chemistry and anatomy. In the year 1972, the Scientific American then published the more recent study titled Brain changes in response to experience which included the contributions of neuroanatomist, Marian C. Diamond. Psychologists predicted that rats in an enriched environment would have increased levels of the chemical Cholinesterase (ChE) in the brain, more specifically, the enzyme known as Acetylcholinesterase (AchE), which is a type of ChE. This chemical is responsible for breaking down Acetylcholine (Ach), which is a neurotransmitter in both the central nervous system and the peripheral nervous system. The purpose of breaking down Ach is to open up the synapse allowing more neuron messages to be passed through. Six different rat species were used, taking 75 littermate pairs, totaling to 150 subjects. Each littermate was randomly assigned to one environment, and its pair was sent to the other. All of the rats used were males, taken approximately 25 days after birth, during the weaning process. At roughly 105 days of age, after 4-8 weeks of living in the environment, the rats were then killed, and decapitated in order to perform a chemical analysis on their brains. The six different rat species were examined in one of two different environmental conditions. The first environmental condition was the condition of environmental complexity and training (ECT), and the second condition was known as the impoverished condition (IC). In the complex environment (ECT), rats lived together in groups of ten to twelve, in larger cages which provided them with toys. These toys were stimulating objects such as swings or

4 Overview and Reflection on Brain changes in response to Experience 4 seesaws. In addition to that, the ECT rats were given daily handling, daily exploration in various mazes, and some formal training in various mazes. Rats that lived in the IC were isolated, living in individual cages with no contact or sight of other animals. Additionally, these rats had reduced illumination in their cages, no opportunity to explore mazes, no formal training with mazes, and had minimal handling (only to take weight measurements). Both environments provided the rats with an unlimited supply of food and water. A third standard environment, which was not mentioned in this publication of the study, was also used for comparison. This standard environment included three rats living together in a basic laboratory cage, which also provided unlimited food and water. (Biological Psychology: An Introduction to Behavioral, Cognitive, and Clinical Neuroscience, 6th Edition. S.M. Breedlove, N.V. Watson, M.R. Rosenzweig, 2010). Once the rats had been decapitated, each one was given a code number, and sent in a randomized order to the chemical analysis laboratory for examination. The codes served the purpose of keeping the environmental group of each rat unidentified. Two of the six species of rat had the cortex of their brain divided into four sections, and the subcortex of their brain divided into eleven sections. The other four species of rat had a four-section cut on the cortex of their brain as well; however, the subcortex was not cut, and instead examined as a whole. Immediately after examination, weight measurements were taken, and each sample was frozen and stored, using dry ice. Psychologists reported the levels of AchE in the rats brains in one of two ways. AchE was either recorded as total activity, or level of AchE activity per unit of weight.

5 Overview and Reflection on Brain changes in response to Experience 5 Where did all of this testing lead psychologists? All of Rosenzweiger s, Bennett s, and Diamond s tests produced results which all proved to be statistically significant at the.05 level in the sensory cortex, and the.01 level in the subcortex. However, the tests also produced results that differed from their original predictions. These psychologists predicted that rats in the embellished environment, or the ECT, would have a higher level of ChE, leaving rats in the IC to have lower levels. These predictions were only partially right. Rats that were kept in the ECT actually had lower overall levels of ChE; however, ECT rats had much higher levels of ChE in the subcortex of their brain. (Effects of Environmental Complexity and Training on Brain Chemistry and Anatomy: A replication. Diamond R.M., Bennett E.L., Krech D., & Rosenzweig M.R. 1962). During the time of this study it made sense that a species living in one particular environment had a start and stop point as far as the development of their brain goes. Psychologists predicted that these rats would either have low levels of ChE or high levels of ChE depending on their environment. What they did not expect to see were varying levels of ChE in different parts of the brain, depending on the rat s environment. ECT rats may have shown lower levels in the cortex of their brain; however they showed much higher levels in their subcortex. Although smaller than the cortex, the subcortex, (which includes the brain stem/beginning of the spinal cord, medulla, cerebellum, reticular formation, thalamus and hypothalamus), is much more vital, and serves a greater purpose. So although IC rats had a higher level of ChE per unit of weight of tissue, this was simply due to the size of the cortex, which his comprised of the four major lobes: parietal, occipital, temporal, and frontal. The cerebral cortex alone makes up 75% of the brain. (Biological Psychology: An Introduction to Behavioral, Cognitive, and Clinical Neuroscience, 6th Edition. S.M. Breedlove, N.V. Watson, M.R.

6 Overview and Reflection on Brain changes in response to Experience 6 Rosenzweig, 2010). Another finding of the ECT rats was that they had a much higher level of glial cells. Glial cells serve the purpose of protecting and nurturing neurons in the brain. (Rosenzweig, M.R., Krech D., Bennett, E.L., & Zolman J.F. Variation in environmental complexity and brain measures. J. comp. physiological psychology, 1962). Why are all of these tests, statistics, and results of brain changes so profound? What does all of this really mean? In order to grasp a full understanding of the content in this study, let s break it down. Psychologists and neurologists had absolutely no idea how complex and moldable the brain was. It was understood that the brain undergoes development, but this development was viewed as an aging process that adhered only to the rules of time and genetics. This study statistically proved what many had only thought of as a mere possibility. We constantly hear how our environment impacts us, but until this very study was published, environmental impacts on the brain were seen as emotional, having more psychological effects, and zero physiological effects. Rosenzweig was very careful to repeatedly state that these statistics were not intended to be applied directly over the human brain; however, they were a basic model of brain change in response to experience. That being said, psychologists were still able to draw basic conclusions from this information. When a rat lived in an environment which provided it with ample opportunity to socialize, learn, and play, it showed greater levels of ChE in its brain, which means it was clearing out room to receive more neurotransmitters. The rat s environment was stimulating the rat s brain to be able to receive more messages; the environment was physically creating more opportunity for the rat to learn more.

7 Overview and Reflection on Brain changes in response to Experience 7 The production of glial cells is of great importance as well. Although the focus of the study was on neurons in the brain and the enzyme ChE, which alters the activity of neurons, glial cells are responsible for protecting them. The production of glial cells was much higher in the ECT rats versus the IC rats. This means that not only were the ECT rats stimulated to clear their synapses, allowing for more neuron messages to pass through, but their environment also stimulated their brain to protect this process, ensuring its occurrence. Every variance test that was published in this study all proved the same effect. Levels of ChE varied among the different species of rats, some being much higher than others, however, every single species had the same effect. Rats living in a complex and enriched environment consistently had higher levels of ChE in their subcortex, and a higher production of glial cells, than the rats that lived in the impoverished environments. These tests provided solid evidence that the environment can directly stimulate change in the brain. References:

8 Overview and Reflection on Brain changes in response to Experience 8 Diamond R.M., Bennett E.L., Krech D., & Rosenzweig M.R. (1962) Effects of Environmental Complexity and Training on Brain Chemistry and Anatomy: A replication and extension Krech, D., Rosenzweig, M.R., & Bennett, E. L., (1962) Relations between brain chemistry and problem solving, among rats raised in enriched and impoverished environments. J. comp. physiological psychology Rosenzweig, M.R., Krech D., Bennett, E.L., & Zolman J.F. (1962) Variation in environmental complexity and brain measures. J. comp. physiological psychology. Rosenzweig, M.R., Kreck D., & Bennett, E.L. (1958) Brain Chemistry and adaptive behavior in H.F. Harlow and C. N. Woolsey, biological bases of behavior. pp S.M. Breedlove, N.V. Watson, M.R. Rosenzweig, (2010) Biological Psychology: An Introduction to Behavioral, Cognitive, and Clinical Neuroscience, 6th Edition. Zolman, J.F., & Morimoto H. (1962) Effects of age of training on cholinesterase activity in the

9 Overview and Reflection on Brain changes in response to Experience 9 brains of maze bright rats. J. comp. physiological psychology Carey B., (2009) Mark Rosenzweig, The Brain Researcher, New York Times publication NY Edition, p22