Neural Mechanisms Of Startle Behavior

In the past fifteen years there has been considerable interest in neural circuits that initiate behavior patterns. For many types of behaviors, this involves decision-making circuits whose primary elements are neither purely sensory nor motor, but represent a higher order of neural pro cessing. Of the large number of studies on such systems, analyses of startle circuits compose a major portion, and have been carried out on systems found throughout the animal kingdom. Startle has been an im portant model because of the reliability of the behavioral act for laboratory study and the accessibility of the underlying neural circuitry. However, probably because of the breadth of the subject, this material has never been reviewed in a comprehensive way that presents the elements com mon to startle circuits in the different animal systems in which they occur. This book presents a diversity of approaches based on a broad back ground of animal groups ranging from the earliest nervous systems in cnidarians to the most recently evolved and advanced in mammals. The behaviors themselves are all short latency, fast motor acts, when consid ered on the time scale of the organism, and involve avoidance or evasion, although in some cases we do not yet completely understand their natural role. These behaviors occur in response to stimuli that have sudden or unexpected onset.

The startle response is a reflexive behavior exhibited by animals as a reaction to threatening stimuli, such as a loud noise or sudden movement. Fish and amphibians exhibit a distinct startle behavior known as a "C-start" that allows them to swim in the opposite direction of a sensory stimulus in order to escape. This action is mediated, in part, by a pair of hindbrain neurons called M-cells. Along with other hindbrain neurons, M-cells relay information from sensory systems to the spinal cord where a motor output is produced. Here, we recorded local field potentials generated by the M-cells and neighboring neurons in the Xenopus laevis tadpole in order to understand the activity of local circuits surrounding the M-cell when it receives visual input from the optic tectum. We described 5 major components of the local field potentials that may correspond to activity from different populations of neurons. We also used pharmacological blockers to determine the influence of different types of transmission on the components. Finally, we looked at the effects of behavioral plasticity on these five components, and showed that habituation to acoustic stimuli had an effect on the mean amplitudes of them. This suggests that these networks may be involved in modulating M-cell activity in response to prolonged sensory stimulation. All together, our findings help us better understand the local circuitry involved in startle response in tadpoles, and how the activity of this circuitry is shaped by behavioral plasticity.

Using the most well-studied behavioral analyses of animal subjects to promote a better understanding of the effects of disease and the effects of new therapeutic treatments on human cognition, Methods of Behavior Analysis in Neuroscience provides a reference manual for molecular and cellular research scientists in both academia and the pharmaceutic