Neural backpropagation

From Wikipedia, the free encyclopedia

This article is about the biological process. For the computer algorithm, see Backpropagation.

Neural backpropagation is the phenomena in which the action potential of a neuron creates a voltage spike both at the end of the axon (normal propagation) and back through to the dendritic arbor or dendrites, from which much of the original input current originated. It has been shown that this simple process can be used in a manner similar to the backpropagation algorithm used in multilayer perceptrons, a type of artificial neural network. In addition to active backpropagation the action potential, there is also passive electrotonic spread.

Contents

[edit] History

Since the 1950s, evidence has existed that neurons in the central nervous system generate an action potential, or voltage spike, the travels both through the axon to signal the next neuron and backpropagates through the dendrites sending a retrograde signal to its presynaptic signaling neurons. This current decays significantly with travel length along the dendrites, so effects are predicted to be more significant for neurons whose synapses are near the postsynaptic cell body, with magnitude depending mainly on sodium-channel density in the dendrite. It is also dependent on the shape of the dendritic tree and, more importantly, on the rate of signal currents to the neuron. On average, a backpropagating spike loses about half its voltage after traveling nearly 500 micrometres.

Backpropagation occurs actively in the neocortex, hippocampus, substantia nigra, and spinal cord, while in the cerebellum it occurs relatively passively. This is consistent with observations that synaptic plasticity is much more apparent in areas like the hippocampus, which controls memory, than the cerebellum, which controls more unconscious and vegetative functions.

The backpropagating current also causes a voltage change that increases the concentration of Ca2+ in the dendrites, an event which coincides with certain models of synaptic plasticity. This change also affects future integration of signals, leading to at least a short-term response difference between the presynaptic signals and the postsynaptic spike[1].

[edit] Functions

There are a number of hypotheses regarding the function of backpropagation of action potentials. In addition to synaptic plasticity, it is also hypothesized to be involved in dendrodendritic inhibition, boosting synaptic responses, resetting membrane potential, retrograde actions at synapses and conditional axonal output.

[edit] Algorithm

While a backpropagating action potential can presumably cause changes in the weight of the presynaptic connections, there is no simple mechanism for an error signal to propagate through multiple layers of neurons, as in the computer backpropagation algorithm. However, simple linear topologies have shown that effective computation is possible through signal backpropagation in this biological sense[2].

[edit] References

  1. ^ Stuart, Greg; Nelson Spruston, Bert Sakmann, Michael Häusser (1997). "Action potential initiation and backpropagation in neurons of the mammalian CNS". TINS 20 (3). 
  2. ^ Bogacz, Rafal; Malcolm W. Brown, Christophe Giraud-Carrier (2000). "Frequency-based Error Back-propagation in a Cortical Network". Proceedings of the IEEE-INNS-ENNS International Joint Conference on Neural Networks, Como (Italy) 2: 211–216. doi:10.1109/IJCNN.2000.857899. 0-7695-0619-4. 
  1. Buzsáki G, Kandel A. Somadendritic backpropagation of action potentials in cortical pyramidal cells of the awake rat. J Neurophysiol. 1998 Mar;79(3):1587-91. PMID 9497436
  2. Bereshpolova Y, Amitai Y, Gusev AG, Stoelzel CR, Swadlow HA. Dendritic backpropagation and the state of the awake neocortex. J Neurosci. 2007 Aug 29;27(35):9392-9. PMID 17728452
  3. Rózsa B, Katona G, Kaszás A, Szipöcs R, Vizi ES. Dendritic nicotinic receptors modulate backpropagating action potentials and long-term plasticity of interneurons. Eur J Neurosci. 2008 Jan;27(2):364-77. PMID 18215234
  4. Waters J, Schaefer A, Sakmann B. Backpropagating action potentials in neurones: measurement, mechanisms and potential functions. Prog Biophys Mol Biol. 2005 Jan;87(1):145-70. Review. PMID 15471594
  5. Bender VA, Feldman DE. A dynamic spatial gradient of Hebbian learning in dendrites. Neuron. 2006 Jul 20;51(2):153-5. Review. PMID 16846850
  6. Migliore M, Shepherd GM. Dendritic action potentials connect distributed dendrodendritic microcircuits. J Comput Neurosci. 2007 Aug 3; PMID 17674173
  7. Lowe G. Inhibition of backpropagating action potentials in mitral cell secondary dendrites. J Neurophysiol. 2002 Jul;88(1):64-85. PMID 12091533
 This neuroscience article is a stub. You can help Wikipedia by expanding it.
Comp Sci logo This computer science-related article is a stub. You can help Wikipedia by expanding it.