PSYC 325 Lecture Notes - Lecture 3: Aplysia, Habituation, Head Direction Cells
27 Nov 2020
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Week 3 Lecture Notes
Jan. 23, 2020
Chapter 3 – Part 2
Habituation, Sensitization and Familiarization
• Brain Substrates
What is going on it there?
Habituation
• A decrease in the strength or occurrence of a behaviour due to repeated exposure to
the stimulus that produces the behaviour
• How does the brain of the rat change so that the same stimulus will now produce a
different behaviour?
• It’s difficult to answer with millions of neurons in the rat brain
Invertebrate Model Systems
• Aplysia californica
o The sea hare
o Has only 20,000 neurons in its CNS
o The neurons are very large and consistent between animals
• These features have made Aplysia popular for understanding the neural mechanisms of
learning and memory
• https://www.nobelprize.org/nobel_prizes/medicine/laureates/2000/press.html
Aplysia Anatomy
Invertebrate Model Systems: Behavior
• Gill-withdrawal reflex:
o Touch the tail, siphon, or mantle.
o 10-12 light touches to achieve full habituation lasting 10-15 min
o The gill contracts within the mantle.
o Time to relaxation and/or amount of contraction is measured.
• Siphon has 24 sensory neurons
• Gill has 6 motor neurons
Habituation and Dishabituation of the Gill-withdrawal reflex in Aplysia
• Gentle touch to mantle produces gill withdrawal
• Progressively smaller (or shorter) withdrawals
• Recovers quickly but, with many sessions, becomes long-lasting
