He demonstrated that the brain continues to form new synaptic connections between nerve cells throughout life in response to environmental enrichment and learning.
[7] During his career, Greenough held a broad range of faculty appointments including psychology, psychiatry, bioengineering, cell and structural biology, and molecular and integrative physiology.
[6] In 2007, he co-edited Defining values for research and technology : the university's changing role, based on a lecture series that began at Illinois in 2000.
[11] The book examines the history of research funding at American universities and the ways in which federal policy had changed.
A shift from public to private sources of funding caused new challenges for universities, financially, strategically, and ethically.
[12][13][14] Prior to Greenough's work, the prevalent belief was that the structure of the brain was determined very early in life and did not change substantially other than to degenerate as a result of damage due to injury, illness, or aging.
[3][2] "The most general conclusion that can be made confidently is that the brain is an extremely plastic organ, the structure of which is exquisitely sensitive to experience.
A major function of the brain is thus to continuously re-organize itself, and it does so in a way that is specifically tailored to result in behavior that is adaptive in the context of the individual’s own unique environment.
In contrast, synapses developing later in life are described as experience-dependent, and are believed to form in response to experiences that result in memories.
[17][19][3] Another researcher describes these processes as "cellular transactions that drive coordinated structural changes in neurons, glia, and blood vessels", essential to understanding the working of long-term memory.
[21][22][23] In summary, Greenough's central contribution was the demonstration that brain development is influenced throughout life by factors such as the environment, exercise and lifelong learning.