Learn is the Process of acquisition of information on spatial and temporal relationships in Environment and also leads to a change in behavioural performance. Memory is The persistence of change in behavioural performance. Non associative is the Simplest type of learning and does not require linking stimuli. Habituation is A decrease in behaviour due to repeated exposure to innocuous stimuli and sensitization is an increase in behaviour due to exposure to a noxious Stimulus. Invertebrates are the best to study cellular activity. A stimulus applied To make the grill of giant marine snail withdrawn into the mantle cavity. Gill withdrawal reflex are larger to stronger Stimulus compared to weak stimulus. Stimulating motor neuron to make change in The gill, EPSP is evoked by sensory neuron. Burst in sensory neuron firing in The motor neuron, lead to reflex contraction of grill. EPSP was measured by Motoneuron L7. The less sensitive of Aplysia synapse can be explained by the Homosynaptic plasticity. Habituation involves an activity dependent presynaptic Depression of synaptic activity. Sensitization of the grill withdrawal reflex. Applying A shock to the tail sensitizes the withdrawal reflex. Short- and long-term nature of sensitization depends On the timing of the application of the shock stimulus. Siphon innervated by 24 Sensory neurons,These in turn connect to 6 motor neurons. Stimulation of the tail acts on three classes of modulatory interneurons.These act on the terminals Of the sensory neurons as well as other interneurons. Serotonergic (5HT) modulatory Action is the most important. Sensitization involves presynaptic facilitation of Synaptic transmission. This allows the animal to remember the shock. A single shock Gives rise to a memory lasting only minutes, and this short-term memory does not Require protein synthesis. Several spaced shocks to the tail give rise to Memory lasting several days. This long-term memory does require protein synthesis.