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Discovering Psychology: Updated Edition

The Responsive Brain

The Responsive Brain is the fourth program in the Discovering Psychology series. This program explores how the brain alters its structure and functioning in response to social situations. You'll learn about the impact of different stimuli on human and animal brains, from the effect of human touch on premature babies to the effect of social status on the health of baboons.

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Experiment: The African Cichlid Fish

Dr. Russell Fernald is a neuroethologist at Stanford University. Neuroethology integrates brain science with the study of behavior in natural habitats. The goal is to illustrate the interaction among brain, behavior, and environment. Dr. Fernald’s long-term work focuses on the African cichlid fish and how its social system regulates not only brain structures, but also bodily functions.

When a male cichlid fish recognizes an opportunity to become the dominant male, his body turns bright colors. The male fish then chases and attacks other male cichlid fish in an attempt to dominate and defend his territory. The physiological color change results from a response in the hypothalamus in the brain. In the cichlid fish, the signaling peptide cells grow eight times larger, sending the brain eight times the signal. The result is an enlargement of the fish gonads, physiologically preparing the fish to spawn with females.

When the cichlid fish loses control of the territory, he loses his bright coloring. Some fish, however, will then go into hiding, turn on the color signals of dominance, and pretend that they are still dominant for a period lasting up to three weeks.

The human brain also contains the hypothalamus. Neuroethologists hypothesize that behavioral responses parallel to those cichlid fish take place in humans, beginning at puberty. Dr. Fernald’s research illustrates one example of how animal and human brains receive and translate signals from the social environment, resulting in physiological change.

The Fernald lab website at has information on current research into the behavior of African cichild fish.


Dendrites: The branched fibers of neurons that receive signals from other neurons. One of the parts of the physical brain known to respond to emotional stimulus, such as touch, by growing and expanding over time.

Neuroethologist: A psychologist who specializes in applying the methodologies of brain science to the study of animal behavior.

Psychosocial Dwarfism: A syndrome in which children’s normal development is inhibited by traumatic psychological surroundings or events. For instance, physical growth may be stunted when young children experience stress due to family trauma, abandonment, or lack of human touch. Also known as stress dwarfism.

Survival of the Fittest: A key concept in the theory of evolution, survival of the fittest can be understood as the idea that those organisms best adapted to their environment will be more successful than those who are not. Although a concept from biology, survival of the fittest, and natural selection began to be used in other spheres as early as 1900.