Sensitisation

Sensitisation

1. Stronger response to stimulus as a result of repeated presentations

2. Can occur because a stimulus is novel or stronger than usual

3. Organism can become hyper-sensitive to a stimulus, rather than habituated to it

4. PTSD may be due to sensitisation

   • Occurs when there's a heightened anx response to an otherwise neutral stimulus

5. Aplysia

   • Sensitisation occurs in different neural circuits to those for habituation
   • Pairing water jet with a noxious electric shock that mimics predatory attack
     • Response to familiar stimulus becomes heightened due to novel electric shock

6. Tail interneuron releases 5-HT onto sensory neuron

   • Water jet still activates sensory neurons, which activates motor neuron to withdraw gill
     • Response is amplified by interneuron's action so it occurs faster
   • 5-HT binds to metabotropic receptor on sensory presynaptic neuron
     • Results in K+ channels being less responsive
       • Less K+ efflux means slower repolarisation
         • Action potentials last longer
           • More Ca2+ influx & more NT release
             • More NT -> Larger depolarisation of postsynaptic motor neuron -> larger gill withdrawal response

7. Long term: increase No. of synapses