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Introduction

Introduction. Ramon y Cajal, 1894

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Introduction

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  1. Introduction • Ramon y Cajal, 1894 • “mental exercise facilitates a greater development of the protoplasmic apparatus and of the nervous collaterals in the part of the brain in use. In this way, pre-existing connections between groups of cells could be reinforced by multiplication of the terminal branches of protoplasmic appendices and nervous collaterals”. • “Textura del Sistema Nervioso del Hombre y los Vertebrados" Joshua T Dudman Raul Rodriguez-Esteban

  2. Introduction (II) • Pavlov, 1903 • Classical conditioning. • Thorndike, 1898 • Instrumental conditioning. Training period: US+CS Test period: only CS Joshua T Dudman Raul Rodriguez-Esteban

  3. Introduction (III) • Behaviorism • Watson, 1913 • Psychology is the “science of behavior”. • Skinner, 1938 • Operant conditioning. Joshua T Dudman Raul Rodriguez-Esteban

  4. Introduction (IV) • Hebb, 1949 • "the problem of understanding behavior is the problem of understanding the total action of the nervous system, and vice versa“ • “Any frequently repeated, particular stimulation will lead to the slow development of a "cell-assembly," a diffuse structure comprising cells in the cortex and diencephalon (and also, perhaps, in the basal ganglia of the cerebrum), capable of acting briefly as a closed system”. • “The Organization of Behavior: A neuropsychological theory” Joshua T Dudman Raul Rodriguez-Esteban

  5. Introduction (V) • Wiesel & Hubel, early 60s • Ocular dominance columns in the mammalian visual cortex. • Woolsey & Van der Loos, 1970 • One barrel-one whisker in the somatosensory cortex of the mouse. Joshua T Dudman Raul Rodriguez-Esteban

  6. Introduction (& VI) • Kandel, 1970-6 • Gill-withdrawal reflex learning in Aplysia due to cAMP synthesis. • Bliss & Lomo, 1973 • Long Term Potentiation in the hippocampus of rats. • Quinn, Harris & Benzer, 1974 • Conditional learning in Drosophyla. Joshua T Dudman Raul Rodriguez-Esteban

  7. Development of patch-clamping Neher & Sakmann, 1976 Joshua T Dudman Raul Rodriguez-Esteban

  8. Whole-cell patch clamp: in vitro slices Characteristics of synaptic connections • Primarily AMPA mediated during basal transmission (~80% at rest) • Connected neurons had 4 to 8 synapses largely on basal dendrites • Average 1.3 + 1.1 mV EPSPs • Average percent failures 14% (20-fold range of values across synapses) Joshua T Dudman Raul Rodriguez-Esteban

  9. Presynaptic Morphology and Release Joshua T Dudman Raul Rodriguez-Esteban

  10. Postsynaptic Receptors (NMDA and AMPA) Joshua T Dudman Raul Rodriguez-Esteban

  11. Coincidence detection by NMDA receptors Joshua T Dudman Raul Rodriguez-Esteban

  12. Induction of long lasting potentiation with a ‘pairing protocol’ • 200 ms pulses of current injected to induce 4-8 spikes pre and post • Post current injection delayed by 1-5 ms to ensure correct timing • Repeated 30 times every 20 seconds during stimulation period Joshua T Dudman Raul Rodriguez-Esteban

  13. Synpatic failures and activity dependent depression • Frequency of synaptic failures indicate of change of synaptic efficacy before and after pairing • Activity dependent depression is altered by the pairing protocol • Test pulses applied with 2nA/5ms current pulses applied at 23 Hz Joshua T Dudman Raul Rodriguez-Esteban

  14. Results • Hebbian learning might involve coding changes, as opposed to only changes in synaptic strength. Joshua T Dudman Raul Rodriguez-Esteban

  15. Results • The coding is mediated by NMDA. • Overall, synaptic gain of strength depends on frequency. • Action potential depression may play only a minor role. Joshua T Dudman Raul Rodriguez-Esteban

  16. Consequences • Low pass filtering Low frequency enhancement. • Phase change. • Energy conservation at high frequencies. • In fact it could be described approx. in terms of RLC circuits (resistors + inductors + capacitors). Joshua T Dudman Raul Rodriguez-Esteban

  17. Remarks • The main effect observed was the reorganization of the synaptic efficacy – other possible consequences were discarded. • In vivo spike discharge is irregular, thus this effect would be of complex result. • Moreover, we cannot know if it really happens in vivo because we need to reach a stationary state to prove it. Joshua T Dudman Raul Rodriguez-Esteban

  18. Remarks • Sejnowski, 1996 • The relationship between memory and this process is not obvious. • The dynamics of the ready releasable vesicles could carry information by themselves – as opposed to only being a limitation. • Could be very important in vision, where plasticity may work as shortly as in 150 ms. • Short-term potentiation vs. LTP influence in short-term dynamics. Joshua T Dudman Raul Rodriguez-Esteban

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