Behavioral components of prey capture in the frog
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2,3
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none of the behavioral components are a necessary prerequisite for the others to occur:
they are independent “FAPs”
If these are FAPs in the true sense the lets find what controls its:
•Step 1 Find cell/s that recognize prey
Laboratory analysis of innate orientation behavior of
toad to varying stimuli
•Toad in glass jar above turntable
•Turntable used to pass targets in front of toad
Results:
•Toad optimally responds to “worm-like” stimuli
•Worm must move along long axis but can move
in any direction
•Orientation responses to worm are consistent
FAPs “they are invariant.”
Sensory transduction: the eye
Sensory transduction: the retina
Rods and cones
(toads rods only)
Bipolar cells
Amacrine cells
Horizontal cells
Ganglion cell
Optic nerve (blind spot)
Sensory transduction: the retina
Synaptic interactions of bipolar, horizontal and amacrine cells produce center surround
fields in ganglion cells
Results from intracellular recordings
Vertebrate ganglion cells in general can be classified into two types
•On-center/off-surround
•Off-center/on-surround
•Additionally, some are sensitive to movement in their field
The retina is a matrix of overlapping center/surround fields of ganglion cells
The search for the cell/s that recognize prey features
Neurophysiological method:
•Animal placed on stage
•Electrodes placed in specific neuropil
•Stimulated visually while recording from cells
Results 1:
Retinal ganglion cells can be typed based on
response type based on size of receptive field:
•R2 4 degrees
•R3 8 degrees
•R4 16 degrees
-no ganglion cell matched behavior
Visual pathway in the toad
Optic nerve crosses at the optic chiasm and projects contralaterally to:
•Optic tectum
•Pre-tectum of the thalamus
Retinotopic organization is maintained in both these regions
Example of Retinotopy from the Macaque visual system
A flickering stimulus
Retinotopic representation in layer 4C of V1
Tootell et al (1988a).
Retinotopic organization is maintained in both these regions
Cross sectional reference
Thalamus
The search for the cell that recognizes prey
Results 2: Thalamic pretectal TH3 cell responses to test stimuli
•Small receptive fields
•Responsive to moving stimuli
•Collectively (as a population) map visual field
•Do not correlate to behavior- are not prey detectors
The search for the cell that recognizes prey
The T5 cell integration of worm features:
•Size
•Shape
•Movement
•2 types defined by different response profiles
T5(2) cells in particular produced invariant responses across changes in a number of
parameters:
•Contrast
•Velocity
•Distance
•So long as the worm-like stimulus moved along its long-axis
The T5(2) response: Putting it all together
Antatomical and physiological organization of TH3, T5(1) and T5(2) cells
T5(1)
TH3
+
-
T5(2)
Output
Output options:
1)
T5(1) HIGH/ TH3 LOW = T5 (2) HIGH
2)
T5(1) HIGH/TH3 HIGH = T5(2) CANCELED
3)
T5(1) LOW/TH3 LOW = T5(2) NO INPUT/CANCELED
4)
T5(1) LOW/TH3 HIGH = T5(2) INHIBITED
So what do you predict would happen behaviorally and in terms of T5(2) cells if you cut the output from
TH3 to T5(2)?
T5(1)
TH3
TH3 lesion
Pre leison
+
-
T5(2)
Output