Neural plasticity

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Under neuronal plasticity is understood the peculiarity of synapses , nerve cells or entire areas of the brain , located on usage in order to optimize their running processes anatomy to change and function. Depending on the system under consideration, one speaks z. B. synaptic plasticity or cortical plasticity.

The psychologist Donald O. Hebb is considered to be the discoverer of synaptic plasticity. In 1949 he formulated Hebb's rule of learning in his book The Organization of Behavior . In the course of the second half of the 20th century, research provided more and more information about the plastic malleability of the brain, even well into adulthood.

Synaptic plasticity

Synaptic plasticity is a term that describes the “activity-dependent change in the strength of synaptic transmission”. These changes can be caused by changes in both the morphology and the physiology of the synapse. Synaptic plasticity is an important research subject in neuroscience , as it is - as has now been directly demonstrated - a neurophysiological mechanism for learning processes and memory .

To explain the term

  • Synaptic activity / transmission: Synapses can be dormant or active. The presynaptic termination is excited at an active synapse , that is, action potentials occur there. It comes to the release of transmitters in the synaptic cleft and their binding to receptors of the postsynaptic membrane . If this triggers a response in the postsynaptic neuron , synaptic transmission has taken place. The answer does not necessarily have to be an action potential, but is often subliminal .
  • Activity dependence: This means that those changes in the synapses are considered that are caused by their activity. In contrast, there are e.g. B. developmental changes in synapses that occur during the growth and differentiation of the nervous system and do not necessarily require synaptic activity.
  • Strength of transmission: This means that a single action potential at the presynaptic endbutton in the postsynaptic neuron can cause a varying degree of change in the membrane potential . The greater this change, the stronger the transmission (and vice versa).

Depending on the duration of the synaptic changes after a certain form of synaptic activation, a distinction is made between short-term and long-term plasticity ( short-term plasticity and long-term plasticity ).

  • Short-term plasticity: The change in transmission strength lasts from a few milliseconds to a maximum of a few minutes.
  • Long-term plasticity: The strength of the transmission changes for many minutes to a few hours, possibly for a lifetime.

The strengthening of synaptic transmission through synaptic plasticity is called potentiation , the weakening is called depression (not to be confused with the clinical picture of depression). Depending on how long it is called long-term potentiation ( long-term potentiation , LTP), short-term potentiation ( short-term potentiation , STP), long-term depression ( long-term depression , LTD) and short-term depression ( short-term depression , HOURS).

Synaptic plasticity can be caused both pre- and postsynaptically .

  • Presynaptic : The amount of the transmitter released per action potential or the speed at which the neurotransmitter is taken up again in the presynaptic cell changes.
  • Postsynaptic : This changes the size of the postsynaptic response to a certain number of transmitters. This happens z. B. by changing the amount of postsynaptic transmitter receptors, by modifying these receptors (often by phosphorylation or dephosphorylation) or by the formation of enzymes that change the behavior of the neurotransmitters in the synaptic cleft.

Pre- and postsynaptic changes can occur simultaneously.

The direction of the change in synaptic transmission and the mechanism by which it occurs is specific to certain synapses and certain types of synaptic activity.

New research suggests that synaptic plasticity, like signal transduction and memory formation in the brain, is based on molecular processes in which reactive oxygen species act as signal transmitters. Their formation - but above all that of peroxide - seems to be controlled by NADPH oxidase .

For the stabilization of synaptic changes, the parallel increase in pre- and postsynaptic structures such as B. axonal bouton , dendritic thorn process and postsynaptic dense membrane region (PSD) play a central role. On the postsynaptic side, the scaffolding proteins PSD-95 and Homer1c are of particular importance. It could be shown that in the case of excitatory synapses of the hippocampus there is a correlation between the extent of permanent enlargement of the dendritic spines and an increase in the proteins PSD-95 and Homer1c.

Cortical plasticity

Cortical plasticity is a term that describes the activity-dependent change in the size, connectivity, or activation pattern of neural networks .

The term cortical plasticity is often used to describe the plasticity of the entire brain, although regions outside of the cortex are also involved, as the principles of cortical plasticity are by no means limited to the cerebral cortex. One consequence of plasticity is that a given function in the brain can “wander” from one place to another. The modern imaging methods have led to a multitude of astonishing observations in that anatomical shifts of function after extensive brain damage have been observed, especially - but not only - in children.

Cortical Plasticity and Cortical Maps

The cortical organization, especially of the perception apparatus, is often referred to as map-like. The sensory perceptions of the foot converge at one point on the cortex and those of the shinbone at another, neighboring point. The result of this so-called somatotopic organization of the sensory impressions in the cortex resembles a map of the body ( homunculus ). These cards are not rigid, but plastic. The lack of sensory impressions from certain parts of the body, for example after an amputation, leads to the fact that the cortical map changes in such a way that the area that was previously responsible for the now missing part gradually changes to the neighboring areas represented in front of existing parts of the body. This can lead to strange false perceptions in the patient during the transition period. Sometimes they feel amputated limbs that are no longer present, because their representation has not yet been completely "erased", but nerve signals from neighboring regions are already penetrating the area of ​​the previous representation of the lost body part.

Cortical maps can change with exercise. For example, Alvaro Pascual-Leone was able to show that the cortical maps of the fingers increased significantly in size after a week after training a piano finger exercise for two hours each day. Anatomical longitudinal studies have shown that three months of juggling training, preparation for the medical physics, but also 40 hours of golf training lead to significant anatomical changes in those brain areas that are entrusted with the control of the practiced skills. Immobilization of the right arm (due to an arm fracture) for 2 weeks also led to a reduction in the cortical thickness in the motor areas that control the mobilized hand or arm.

After research had shown that outstanding abilities in sports, art and science also arise from intensive and frequent exercise, essential conclusions were drawn about neuroplasticity from neuroanatomical and neurophysiological comparisons of trained and non-trained persons. Studies have shown that trained people have anatomical and functional peculiarities, especially in those areas of the brain that are associated with the control of the trained person. These anatomical abnormalities are associated with morphological changes in the synapses, the neuropil and the neurons. Above all in professional and semi-professional musicians, diverse anatomical and functional abnormalities have been found that can be attributed to neuroplasticity.

See also

literature

  • Lutz Jäncke : Textbook Cognitive Neuroscience . Huber Verlag, Bern 2013, ISBN 978-3-456-85004-7 , pp. 595–623.
  • Manfred Spitzer : Spirit on the Net . Spektrum Akademischer Verlag, Heidelberg 1996, ISBN 3-8274-0109-7 , pp. 148-182.
  • Norman Doidge: The Brain That Changes Itself . Viking, New York 2007 (German: Neustart im Kopf: how our brain repairs itself . Translation by Jürgen Neubauer. Campus-Verlag, Frankfurt am Main / New York 2008, ISBN 978-3-593-38534-1 .)
  • New start in the head. Film directed by Mike Sheerin, Norman Doidge. (Canada & France 2009, 70 min, Arte F) German first broadcast Arte November 18, 2009.
  • Johann Caspar Rüegg : Neuronal plasticity and psychosomatics (1) . In: Reinhold Haux, Axel W. Bauer , Wolfgang Eich, Wolfgang Herzog , Johann Caspar Rüegg, Jürgen Windeler (eds.): Science in medicine. Part 2. Physiology and Psychosomatics. Attempts at approximation (=  bridges ... writings on interdisciplinarity . Volume 4 ). VAS, Frankfurt am Main 1998, ISBN 978-3-88864-249-4 , p. 82-120 .
  • Gerd Rudolf : Neural plasticity and psychosomatics (2) . In: Reinhold Haux, Axel W. Bauer , Wolfgang Eich, Wolfgang Herzog , Johann Caspar Rüegg, Jürgen Windeler (eds.): Science in medicine. Part 2. Physiology and Psychosomatics. Attempts at approximation (=  bridges ... writings on interdisciplinarity . Volume 4 ). VAS, Frankfurt am Main 1998, ISBN 978-3-88864-249-4 , p. 121-130 .

Web links

Individual evidence

  1. ^ Donald Oding Hebb: The Organization of Behavior: a neuropsychological approach . Wiley, New York 1949.
  2. G. Yang, CS Lai, J. Cichon, L. Ma, W. Li, WB Gan: Sleep promotes branch-specific formation of dendritic spines after learning. In: Science. 344 (6188), 2014, pp. 1173-1178. PMID 24904169
  3. KT Kishida, E. Klann: Sources and Targets of Reactive Oxygen Species in Synaptic Plasticity and Memory. In: Antioxidant Redox Signal . 9, 2007, pp. 233-244. PMID 17115936 .
  4. ^ D. Meyer, T. Bonhoeffer , V. Scheuss: Balance and Stability of Synaptic Structures during Synaptic Plasticity . In: Neuron . tape 82 , no. 2 , 2014, p. 430–443 , doi : 10.1016 / j.neuron.2014.02.031 , PMID 24742464 .
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  9. L. Bezzola, S. Merillat, C. Gaser, L. Jäncke: Training-induced neural plasticity in golf novices. In: Journal of Neuroscience. 31 (35), 2011, pp. 12444-12448.
  10. N. Langer, J. Hänggi, NA Müller, HP Simmen, L. Jäncke: Effects of limb immobilization on brain plasticity. In: Neurology. 78 (3), 2012, pp. 182-188.
  11. ^ KA Ericsson, RT Krampe, T. Clemens: The role of deliberate practice in the acquisition of expert performance. In: Psychological Review. 100 (3), 1993, pp. 363-406, PDF .
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  14. TF Munte, E. Old Muller, L. Jäncke: The musician's brain as a model of neuroplasticity. In: Nature Reviews. Neuroscience. 3 (6), 2002, pp. 473-478.
  15. ^ L. Jäncke: Music drives brain plasticity. In: F1000 Biology Reports. 1, 2009, pp. 1-6.