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Environment Shapes Auditory Processing
by Navzer Engineer, Cherie Percaccio and Michael Kilgard
Brains of both animals and humans are 'plastic' throughout one's lifetime
This plasticity or the capacity for the brain to change is strongly influenced by environmental conditions. Over the years, it has been demonstrated that enriched environments increase brain thickness, the number of neurons, and the number of connections between neurons (for a review, see van Praag et. al., Nature Neurosci. Reviews, Dec 2000.) Many of these changes were observed in the cerebral cortex, the wrinkled gray matter covering of the cerebrum. But how does environment affect brain responses? The so called 'primary areas' of the cerebral cortex process sensory information (touch, sight, smell, and hearing.) The auditory cortex, located in the temporal region of the brain is responsible for the processing of sounds. In our study (Engineer, Percaccio et. al., J. Neurophys., March 2004,) we wanted to find out whether environmental conditions influence neurons in the auditory cortex of young and adult animals in response to sound. We were also interested in the time course of these changes; for example, what would happen to auditory cortex responses when animals are switched from an enriched condition to a standard condition and vice versa?
Rats were reared in standard or enriched housing conditions. In the standard condition, rats were housed two per cage. They were not deprived of sensory stimulation. Their acoustic environment consisted of vocalizations from 20-30 other rats housed in the same room, and sounds resulting from daily room traffic, feeding and cleaning, which were also heard by the enriched group. On the other hand, sounds in the enriched environment were more diverse and provided more behaviorally relevant information than the sounds in the standard condition. Our enriched environment included a rich variety of visual, auditory and tactile stimuli compared to the 'boring' standard environment. In the enriched environment, 4-8 rats were housed together in a single large cage. Chains, wind chimes, or bells were hung across different levels of the cage so that a unique sound was elicited when rats passed from one level to the next. A motion detector emitted a chime each time a rat crossed an infrared beam in front of a water source. An exercise wheel emitted a tone and activated a small light with each rotation. Each movement-triggered sound had unique characteristics that provided behaviorally meaningful information about the location and activity of other rats in the cage. A CD player presented randomly selected sounds every 2 to 60 seconds. These sounds included simple sounds (tones) and complex sounds (rat vocalizations, classical music, rustling leaves, etc.) Some of the sounds were paired with a reward (sugar pellet) to encourage attention to the sounds. These sounds were provided 24 hours a day.
Two techniques were used to document changes in the brains responses to sounds. In the first experiment, rats were anesthetized after 2 months of enrichment, which allowed us to record the responses of individual auditory cortex neurons to sound. In the second experiment, we recorded the average activity of many neurons from awake rats each week during the course of enriched or standard housing. This technique allows us to follow the time course of brain changes in individual animals as we changed their environment. Similar recordings can also be made in humans.
Our major finding was that enrichment dramatically increased the strength of auditory cortex responses. When we followed the time course of these changes, we observed that in early enriched rats (housed in the enriched condition before the standard condition,) responses were twice the size of the standard housing group after just a few weeks. When this group was transferred to the standard environment, responses decreased by as much as 60% within a week of moving to the boring environment. Our study shows that:
1) cortical responses of both young and adult animals benefit from exposure to an enriched environment and are degraded by exposure to an impoverished environment; and
2) these changes occurred rapidly within days of moving. Enrichment also made primary auditory cortex neurons more sensitive to quiet sounds and more selective for tone frequency.
This study could not determine what specific components of the environment (social experience, behavioral relevance of sensory events, attention, physical activity, or enrichment duration) were important for altering cortical responses. These topics are now being addressed in a follow-up study. Our study extends earlier research showing that environmental conditions can stimulate physical changes in the brain by revealing how similar experience specifically alters processing of auditory information .
Enrichment, learning and education: Lessons from animal research
It is no longer believed that the brain stops changing once development is over. Even in adulthood, new connections between neurons are constantly being made, new neurons are being born and brains can reorganize and adapt to novel environments over short time scales. Neuroscientists are not the only ones who are fascinated by the brain and its capacity to change. More and more educators and teachers are starting to realize that neuroscience research can contribute to understanding why learning environments are so important for building healthy brains. How can we apply this research in animals to improving education? These results confirm most teachers' intuition that the rich, stimulating environments they provide really do make a difference and indicate that boring environments may actually have negative consequences on the brain. While it is difficult to extrapolate knowledge gained from neuroscience to immediate classroom application for children, we can at least begin to appreciate that brains of both children and adults, just like that of animals, are plastic and can rapidly reorganize in different environments.
Environmental Enrichment Improves Response Strength, Threshold, Selectivity, and Latency of Auditory Cortex Neurons Navzer D. Engineer, Cherie R. Percaccio, Pritesh K. Pandya, Raluca Moucha, Daniel L. Rathbun, and Michael P. Kilgard. J Neurophysiol, March 10, 2004.
Navzer D. Engineer has an M.D degree and a master's degree in Cognition and Neuroscience. Currently, he is working towards a Doctorate in Neuroscience in the Department of Behavioral and Brain Sciences at the Unversity of Texas at Dallas where he works in the Cortical Plasticity Laboratory of Dr. Michael Kilgard.He is interested in how enriched enrivonments and behavioral training facilitate learning and plasticity in cortical neurons. navzer@utdallas.edu
Cherie R. Percaccio M.S., M.S. is a Doctoral Candidate in Communication Sciences/Cognition and Neuroscience at the University of Texas at Dallas; Richardson, TX. Dr. Michael Kilgard is her research advisor. revielle@utdallas.edu
You can find out more about Dr. Micheal Kilgard here: http://www.utdallas.edu/~kilgard/cv.html
Lab Website: www.utdallas.edu/~kilgard
©June 2004 New Horizons for Learning
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