Mechanisms Of Synaptic Plasticity

Mechanisms of synaptic plasticity     Two mechanisms: o New synapses are produced (or old one are “pruned”). o Individual synapses are strengthened. Postsynaptic and presynaptic strengthening are both due to action of calcium signal. Postsynaptic strengthening: o Insertion of new AMPA receptors in postsynaptic membrane. o Receptors are proteins; could be built as needed, but this would take time. o Evidence suggests that the receptors have been preassembled in storage location. o When LTP is produce, they are moved into place on the postsynaptic membrane. o This requires the action of Ca2+-dependent enzyme called CaM-KII. Presynaptic strengthening: o Activation of NO synthase post-synaptically leads to production of NO. o NO diffuses through the cell membrane and acts as a retrograde messenger. o Activates enzymes in the presynaptic terminal; results in increased release of neurotransmitter. Learning  Process by which we acquire knowledge about the world.  Refers to a more or less permanent change in behaviour which occurs as a result of practice.  Either a case of differential strengthening of one from a number of responses evoked by a situation of need, or the formation of receptor-effector connections de novo; the first occurs typically in simple selective learning and the second in conditioned reflex learning. Perceptual learning  Most obvious when familiar things change (e.g. when a friend you’ve known for years suddenly shows up with glasses).  Perception occurs in the sensory association cortex: o Visual object recognition is in the inferior temporal cortex. o Electrical stimulation of this area elicited vivid visual memories in human patients undergoing brain surgery. o Damage results in a loss of ability to recognise objects (visual agnosia), although vision itself is not impaired. Classical conditioning       Fear conditioning paradigm: o Conditioned stimulus (CS): neutral; does not cause fear. o Unconditioned stimulus (US): fear-eliciting; causes fear (UR) o When paired together, CS is able to cause fear (CR). Little Albert showed no fear of a white lab rat until it was paired with a fear-eliciting loud noise (Watson and Raynor). LeDoux experimented on emotional learning. The fear conditioning paradigm – the conditioned emotional response. To find the area in the brain underlying this condition, two conditions must be met: o Information about both the CS and US o The area must have something to do with the production of the UR (fear). Role of the amygdala and fear: o Kluever and Bucy showed in the 1930s that removal of the temporal lobe in monkeys resulted in a profound taming. o Later, it was shown with rats that this was due to destruction of the amygdala. o Activation in the basolateral amygdala occurs within a second of a fear-eliciting stimulus. o In Urbach-Wiethe disease (genetic disorder), in addition to changes in the skin and mucous membranes, there is degeneration of the amygdala. Patients were shown clips of     Doris Day screaming but were unable to understand what she was doing; problems with deciphering negative emotions. However, no problems with positive emotions and recognising familiar faces. o Benzodiazepines work on the amygdala, causing an anxiolytic effect. How the amygdala organises a fear response. How you react to danger without thinking. The input to the central nucleus comes from other nuclei of the amygdala. LeDoux conditioned rats by pairing a tone CS with an electric shock US.