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LTP - PowerPoint PPT Presentation

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LTP. Overview. LTP as candidate mechanism for (Hebbian) learning in the brain at the level of neurons Hippocampus overview LTP, an introduction LTP mechanisms LTP studies (proof of LTP mechanisms). Learning.

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  • LTP as candidate mechanism for (Hebbian) learning in the brain at the level of neurons

  • Hippocampus overview

  • LTP, an introduction

  • LTP mechanisms

  • LTP studies (proof of LTP mechanisms)


  • Where does learning take place at the neuronal level? What do we mean when we say neurons are plastic?

  • Neurons are plastic at the synapses.

  • Change in synaptic connectivity might constitute the mechanism of learning

Hebbian learning
Hebbian Learning

  • "when an axon of cell A ... excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased" (Hebb, 1949)

  • Cells that fire together, wire together

Hebbian learning continued
Hebbian Learning, Continued







“Hebbian” learning






Mechanism for hebbian learning
Mechanism for Hebbian Learning

  • LTP is a candidate mechanism for Hebbian learning (synaptic plasticity)

  • LTP is a persistent increase in synaptic strength (as measured by the amplitude of the EPSP) that can be rapidly induced by brief neural activity

Where does ltp occur
Where does LTP occur

  • LTP has been found in mammalian neocortical regions, and in subcortical nuclei

  • LTP has also been found in the peripheral nervous system of mammals

  • LTP has mainly been studied in the hippocampus, a vital structure for memory

Histological section of hippocampus
Histological Section of Hippocampus


EC = Entorhinal Cortex

S = Subiculum

DG = Dentate Gyrus

CA3 = CA3 field

CA1 = CA1 field

(PrS = PreSubiculum)

(PaS = ParaSubiculum)

Neurogenesis an aside
Neurogenesis, An Aside

  • The dentate gyrus continuously creates new neurons!

  • New neurons necessary for learning across time delays (Shors et al, 2001)

  • New neurons necessary for generating random context which minimizes interference, creates distinct codes (Becker, 2005)

Original ltp study
Original LTP Study

  • By Timothy Bliss and Terje Lomo (1973)

  • Done on an anaesthetized rabbit’s hippocampus

  • Brief, high-frequency stimulation of the perforant pathway input to the dentate gyrus produced a long lasting enhancement of the extracellular recorded field potential

General ltp experimental design
General LTP Experimental Design

Stimulation of a bundle of presynaptic axons

Recording of monosynaptic EPSP

Typical results
Typical Results

Typical Results

Ltp recording techniques
LTP Recording Techniques

  • In Vivo – in live animals

  • In Vitro – slice preparations, taken out of animal and manipulated in lab

  • Extracellular recording – multiple neurons

  • Intracellular recording – single neuron

Properties of ltp
Properties of LTP

  • Rapid

  • Long Lasting effects

  • Specificity

  • Co-operative

  • Associative

How does ltp work
How Does LTP Work?

  • LTP requires some sort of additive effect

    • High-frequency stimulation

  • Activation of synapses and depolarization of the postsynaptic neuron must occur at the same time

  • LTP additive effect takes place due to workings of glutamate receptors


  • Glutamate is an excitatory neurotransmitter in CA1

  • There are two kinds of glutamate receptors: AMPA and NMDA

  • AMPA receptors are simple – the presence of glutamate opens channels for sodium (Na+) ions.


  • Mg2+ blocks ion channel

  • When cell is depolarized, Mg2+ forced away

  • Ca2+, as well as Na+, can enter through ion channels