Behavioral Neuroscience, lecture on Turtles and Eyeblink behavior
Eyeblink Conditioning
I. Pond Turtles
A. Chrysemys picta (Painted Turtle) or C. scripta (Red-eared Pond Slider) are relatively large
aquatic turtles
1. Habitat: slow moving shallow streams, sluggish rivers,
swamps, ponds, lakes
a. soft bottoms, vegetation, half submerged logs
b. C. picta = most widespread turtle in North America
i. bicoastal in the north, eastern in south
(1) few populations in SW
c. C. scripta = eastern U.S. - Virginia to Brazil
2. reptiles in freshwater habitats with few amphibious habits
a. unlike other turtles cannot derive much O2 from water
b. court in the water
i. lay eggs in moist pits on land
c. bask in the sun
i. to increase metabolic rate
d. use celestial cues for directional guidance
3. herbivorus as adults
a. juveniles eat insects and other invertebrates
4. very long lived
a. sexual maturity only after 2-8 years
5. Evolutionarily very old - Miocene > 5(10)6 years
Cenozoic Era 65 mya - present, Tertiary Period 65-1.8 mya, Miocene Epoch 23-8-5.3 million years ago
B. Turtle Eye Blink
1. nictitating membranes, or 3rd eyelids
a. addition to their normal eyelids in some animals
i. turtles and some mammals
2. Aquatic environments with vegetation have a variety of potential
hazards for the eyes
a. nictitating membranes are translucent but protective
3. in response to a corneal stimulus
a. imagine entering the water
b. or some dust on an air current moving toward the eye
4. the eyeball is retracted into the orbit
and
5. the nictitating membrane is actively moved across the eye
a. by the pyramidalis and quadratus muscles
b. eyeball retraction is not required for the blink
6. most experiments use an airpuff to the cornea of rabbits or cats
a. the blink is a passive sweeps across the eye
b. due to retraction of the eye by extraocular muscles
II. Eye Blink Reflex (rabbits, cats, mice)
A. Sensory information from the face
1. Trigeminal nerve afferents
a. opthalmic branch
b. to the spinal fifth cranial/trigeminal nucleus
B. One interneuron in trigeminal complex
1. nucleus oralis
a. disynaptic pathway
C. stimulate accessory abducens nuclei motor nerve fibers
1. innervate retractor bulbi muscle
a. contraction pulls eye into socket
i. passive blink
D. trigeminal also stimulates facial, principle abducens,
oculomotor and trochlear nuclei
1. facilitates eye retraction
a. simultaneous contraction of all extraocular muscles
(except superior oblique)
2. turtles don't have orbicularis oculi muscle
a. \ facial nerves not involved
E. Conditioning: US = airpuff, CS = sound
1. training pair airpuff with sound
2. CR = rabbit will blink to sound alone
3. Cerebellum is important for conditioning
a. lesions in cerebellum disrupt the acquisition and
retention of a classically conditioned eyeblink reflex
i. lesion to cerebellar vermis abolishes CR but not UR
(1) learning depedendent activity of vermis
neurons parallel conditioning
ii. lesion to deep interpositus nucleus
of the cerebellum also abolishes CR