The biology of behavior

How does a bluejay remember where it stored a tasty seed through the winter? How does a hunted mouse recall the shortest route to the safety of its burrow? It all comes down to spatial memory, the mental map that keeps both animals and humans headed in the right direction.

Some Div. 6 (Behavioral Neuroscience and Comparative Psychology) members seek to answer these questions by studying animals' spatial memory, while others investigate subjects including perception, learning and their biological underpinnings. Their topics are varied, but they all seek to deduce the forces that shape behavior.

In the case of spatial memory, "we not only want to understand...how the circuits in the hippocampus and cortex change as a result of these memories, but we also want to understand how memory is influenced by evolution," says Div. 6 President Karen Hollis, PhD, a psychology professor at Mount Holyoke College. "Why do some species have better spatial memory than others?"

Fully understanding spatial memory will take an attack on multiple fronts. For instance, behavioral neuroscientists Karyn Frick, PhD, and Michela Gallagher, PhD, study the brain mechanisms that underlie spatial memory in rodents, and Alan Kamil, PhD, takes an evolutionary perspective on spatial memory in seed-storing birds.

Caged and aged

Michela Gallagher, PhD, department chair at Johns Hopkins University's Department of Psychological and Brain Sciences, studies the effects of aging on rats' spatial navigation abilities. She's found that, over time, some rats become impaired while others continue to perform food-seeking and escape tasks as well as young animals. These dramatic individual differences mirror what's known about human aging, says Gallagher.

To explore why age treats animals so differently, Gallagher examines rats' medial temporal lobe and hippocampus, and has found differences between impaired and nonimpaired animals' brain function, but she hasn't found evidence of cell loss. This discovery, published in the Proceedings of the National Academy of Science of the United States of America, (Vol. 93, No. 18, pages 9,926-9,930) counters the commonly held belief that brain degeneration causes the cognitive impairments of normal aging, she says.

In fact, some impairment may even be caused by too much brain activity. In a recent study, published in The Journal of Neuroscience, (Vol. 25, No. 29, pages 6,877-6,886), Gallagher was surprised to find hyperactivity in the part of the hippocampus known as the CA3 region. That area allows the brain to encode new information separately from old information, though too much activity there could actually hinder information processing, Gallagher suspects.

"There are a whole series of studies published...in people over 55 who are diagnosed with mild cognitive impairment...and they show more hippocampal hyperfuction than age-matched controls do," she says. Gallagher tests certain drugs, including valproate-a drug used to treat epilepsy and bipolar affective disorders in humans-on her rats to see if she can control their brain hyperactivity. It's research that could eventually lead to treatments for aging humans.

"I think there is a lot of potential connection and interplay between the human and animal research in the study of cognitive aging," she says.

Turning back the clock

Karyn Frick, PhD, an associate psychology professor at Yale University, is also making connections between human and animal aging, through research on the effect of hormones on spatial memory in aged female mice. When mice age, their estrus cycle stops in a way that's analogous to human menopause. When this happens, they begin to show spatial memory decline, says Frick, who tests the performance of ovariectomized mice in a Morris water maze.

In a 2006 study published in Pharmacology Biochemistry and Behavior (Vol. 81, No. 1, pages 112-119), Frick reported that when she injects these impaired mice with estrogen, the animals' memory improves. Estrogen alters key synaptic proteins in the hippocampus and neocortex, which suggests that it enhances memory by augmenting synaptic plasticity, says Frick.

Frick's work may inform the current debate over hormone replacement for menopausal women.

"These hormones were on the market to relieve menopausal symptoms, but they then had the side effect of affecting cognition in some people," she says. "Basic research on cognition wasn't done when women were taking these things, and now we're backtracking to figure out what these hormones do to the brain and behavior."

Frick hopes that her research will help physicians and patients make better-informed decisions about hormone-replacement treatment.

Of course, hormones aren't the only path to better memory. Recently, Frick has used environmental enrichment-in the form of many novel toys-to improve memory in her older mice. She's found that a combination of enrichment and exercise is even more effective than hormone replacement for improving memory-a finding that could lead to interventions for humans.

"Ultimately, no one is interested in whether hormones do anything to an old mouse brain," she says.

Brainy birds

Bird brains might also provide insights into human memory, says Alan Kamil, PhD, a professor of biology and psychology and the director of the School of Biological Sciences at the University of Nebraska-Lincoln. Kamil studies the spatial memory of seed-caching birds, such as nutcrackers, crows and jays, as they hide food for future retrieval. Studies of natural caching behavior suggest that some of these birds remember five or six thousand locations for up to nine months.

The birds may use the sun as a compass, but they may also use directional relationships (or bearings) between landmarks such as rocks, trees or buildings and the goal, says Kamil in a report in the Journal of Experimental Biology (Vol. 204, No. 3, pages 103-113). Kamil tests this hypothesis in the lab by burying seeds in a room full of sand while manipulating objects that stand in for landmarks.

"If the landmarks are reasonably spread out, they define a triangle and the place you are looking for is within the triangle," he says.

Kamil has also shown that birds that are more dependent on stored food, including corvids such as crows, jays and nutcrackers, have better spatial memory than birds that don't rely as much on a cached food supply.

Such studies bridge biology and psychology, Kamil says.

"I've been arguing to psychologists that biology and natural history and evolutionary pressures are important factors...in our study of cognition, and I would argue to biologists that the ability to learn and remember is an essential part of what they want to understand about animals."

Div. 6 at a glance

Div. 6 (Behavioral Neuroscience and Comparative Psychology) members study behavior and its biological underpinnings. Specifically, behavioral neuroscientists link the inner workings of the brain to behavior and other body systems. Comparative psychologists study similarities and differences in the behavior of humans and other animals, aiming to shed light on evolutionary and developmental processes. Members receive the division's newsletter, The Behavioral Neuroscientist and Comparative Psychologist three times a year. For more information on Div. 6, visit www.apa.org/divisions/div6.