Grant: Discovery Grants Program - Individual

The highest level of the brain of all mammals is the cortex and the human cortex is vastly larger than that of other mammals, including those of the great apes. Cortex is composed of billions of "neurons", cells specialized for processing external sensory input such as vision and sound and controlling muscles for directed movements. The cortex is also responsible for learning and memory. There are literally hundreds of different types of neurons in cortex. Cortical neurons are organized in a very complicated manner and different neurons are organized into layers. Each layer contains many different types of neurons. Cortical neurons are strongly interconnected to form a "recurrent network" but how this network operates has proven too difficult to analyze. As a result, we have minimal understanding of how cortex works to enable our high-level cognitive abilities - thinking, remembering, planning and deciding; this means that we have minimal understanding of how to treat neurologic or psychiatric disorders affecting thought, decision making and memory. Our research tries to figure out how a similar but much simpler structure can support the apparently simple ability to visually discriminate objects and remember the location of food and home. The structure is the pallium- the highest level of the fish brain. Like cortex, pallium contains highly interconnected neurons, i.e., it is a simple recurrent network. However, unlike cortex, pallium is tiny and contains only one type of simple neuron. With such a simple pallium, fish can only recognize simple shapes and have a memory for food location extending only days rather than years. My research aims at understanding the fundamental properties of the recurrent network of fish pallium and how they can, for example, discriminate between the simplest shapes - vertical versus horizontal stripes. We will use experimental tools to understand how individual neurons work and how they interact as the fish recognizes a stimulus. This will at least give clues as to how the vastly more complicated human cortex works and therefore give clues as to how to treat disorders of cortical function. We use zebrafish for our studies because their brain development is well understood and has many similarities with the development of mammalian brains. Our result will therefore be entirely applicable to our understanding of human brains. We use juvenile (3-4 weeks old) male and female zebrafish in our studies and there are no discernable sex differences in these non-breeding fish. Future work will, however, use breeding fish. We are specifically interested in whether the fish's sex will affect how its pallium operates during visual discrimination tasks.