Lectures for Animal Behavior

Animal Behavior - Biology 4200/5430

Bowling Green State University, Fall 2009

Orchestration of Motor Responses

"I am coming more and more to the conviction that the rudiments of every human behavioral mechanism will be found far down in the evolutionary scale and also represented even in primitive activities of the nervous system" -- Karl Lashley, 1951

Neuroethology

We are most likely to find a clear role of the nervous system in the control of behavior when we focus on those behaviors in which the brain does a minimum of processing. Primary examples may therefore not always deal with the most interesting types of behavior. Alternatively we can deal with those systems where functions are limited to one primary goal and which are highly optimized to achieve it. this is particualrly true for sensory systems which encode a single stimulus parameter. Alternatively we can examine motor programs where we can ask how a particular behavior is produced, starting from the motor centers, working our way upstream in the flow of information processing, until we reach the mechanisms contributing to the sensory input ends.

Executive control

Central programs generate stereotyped motor responses - <Fixed Action Patterns>.

Command Neurons vs. Central Pattern Generators

<Command neurons>: cells, when activated, are capable of producing complex behavior patterns in the absence of any meaningful external stimuli. Activation of the neurons is both necessary and sufficient. Is this an outdated concept? Neurons cannot be viewed as single identities, they are imbedded within circuits and their activity only makes sense within the context of such circuits.
- mating song in crickets
- giant fibers in crayfish escape circuitry, single spikes sufficient for behavior
- Mauthner neurons in goldfish
Central Pattern Generators. Example: Stomatogastric system of crustaceans

Crayfish Escape Behavior

Neural structures in crayfish. (A) Lateral view; (B) Dorsal view; (1) Brain (cerebral ganglion) (2) Circumesophageal commissure; (3) Subosophageal ganglion; (4) Thoracic ganglion; (5) Abdominal ganglion; (6) Esophagus; (7) Sternal artery; (8) Anus; © Loretto Zoology

Bipolar sensory neurons: tuned to touch or high frequency water movements (>80Hz) - sensory filtering.
Sensory neurons produce chemical synapses onto non-giant interneurons, and electrical synapses to giant interneurons
subthreshold stimulation triggers non-giant escape swimming, produced by a pattern generator consisting of interneuron networks
Medial Giant Interneurons: brain to last abdominal ganglion, contraction of fast flexor muscles in all abdominal segments, direction of escape: straight back
Lateral Giant Interneurons: segmentally repeated; input in abdominal segments, flexor contraction in anterior segments of abdomen, direction of escape: upwards
giant motor neurons and fast flexor motor neurons for flexion of abdomen via giant fibers
Non-Giant Interneurons: escape swimming
Habituation only occurs if stimulation of sensory neurons is sufficiently intense to drive an action potential in the giant fiber system
Re-Extension of abdomen follows lateral giant tailflips within 100ms of stimulus, reflex of hair receptors and muscle receptor organs
Excitation of extensor systems via excitatory interneurons with onset of tailflip to prepare for re-extension
Inhibition of extensor systems via inhibitory interneurons while tailflip is happening
then Inhibition of further tailflips while re-extension is happening: inhibition of sensory neurons driving giant fibers, inhibition of flexor muscles

Film

Crayfish escape behavior: tailflips

Reading Assignment

Chapter 7: The Nervous System and Behavior

WikiBooks

Motor systems

Links of interest

last modified: 10/24/03