The ability to stimulate plasticity in the adult brain would provide a means to enable patient recovery from a variety of insults and conditions including stroke, amblyopia, and neurodegenerative disease. In this recent correspondence, Lunghi and Sale report that intermittent exercise by human subjects during a brief visual system challenge can significantly enhance a shift in perception that occurs with visual challenge alone. When presented with incongruent images to each eye, subjects report alternating perception of each of the two images, a phenomenon termed binocular rivalry. Following a brief period of monocular deprivation (MD), subjects report increased perception of images presented to the deprived eye. Lunghi and Sale report that this shift is more pronounced if subjects perform intermittent exercise during the MD period. Paralleling studies in experimental models in which environmental modification can stimulate visual system plasticity in the adult brain (He et al., 2007; Sale et al., 2007), these data suggest that exercise can enhance plasticity in the human brain in ways that could be harnessed to overcome deficits produced by disease.
This study raises a number of interesting issues. The authors compare the shifts in perception that subjects exhibit during binocular rivalry to plastic shifts in ocular dominance (OD) described in experimental animals following MD. OD, the relative strength of responsiveness of the visual cortex to input from each eye, is most flexible during a critical period of postnatal development, though a number of different manipulations can greatly enhance this plasticity in adulthood (reviewed in Hubener and Bonhoeffer, 2014). However, shifts in perception of binocular rivalry occur much more quickly than do OD plasticity shifts (Gordon and Stryker, 1996) and more quickly than homeostatic changes thought to contribute to OD plasticity in experimental models (Keck et al., 2013; Mrsic-Flogel et al., 2007). Whether the more rapid change in binocular rivalry is due to plasticity at a smaller, more malleable set of synapses, or it represents a different kind of adaptation, is an important question when considering how these findings relate to plasticity in the brain more broadly. Though enhanced with exercise, the shift in binocular rivalry can occur in the absence of exercise, raising the possibility that this adaptive ability of the cortex may be present and constant throughout life and less analogous to other forms of cortical plasticity that are more difficult to engage in adulthood.
How does exercise modulate the plasticity of binocular rivalry? In mice, running has been demonstrated to enhance primary visual cortical responses to visual input (Niell and Stryker, 2010), at least in part through the modulation of inhibitory circuitry (Fu et al., 2014). In the current study, exercise may induce a more robust shift in rivalry post-challenge by increasing the magnitude of visual cortical responses during MD. Whether this effect is short-lived and/or represents a type of plastic change that could be harnessed to rewire damaged or dysfunctional cortex is an important question. Along with a better understanding of the circuit-level basis for the phenomenon described in this study, future studies should provide a clearer picture of the potential for exercise to enhance adult plasticity more broadly.
References:
Fu Y, Tucciarone JM, Espinosa JS, Sheng N, Darcy DP, Nicoll RA, Huang ZJ, Stryker MP.
A cortical circuit for gain control by behavioral state.
Cell. 2014 Mar 13;156(6):1139-52.
PubMed.
Gordon JA, Stryker MP.
Experience-dependent plasticity of binocular responses in the primary visual cortex of the mouse.
J Neurosci. 1996 May 15;16(10):3274-86.
PubMed.
He HY, Ray B, Dennis K, Quinlan EM.
Experience-dependent recovery of vision following chronic deprivation amblyopia.
Nat Neurosci. 2007 Sep;10(9):1134-6. Epub 2007 Aug 12
PubMed.
Hübener M, Bonhoeffer T.
Neuronal plasticity: beyond the critical period.
Cell. 2014 Nov 6;159(4):727-37.
PubMed.
Keck T, Keller GB, Jacobsen RI, Eysel UT, Bonhoeffer T, Hübener M.
Synaptic scaling and homeostatic plasticity in the mouse visual cortex in vivo.
Neuron. 2013 Oct 16;80(2):327-34.
PubMed.
Mrsic-Flogel TD, Hofer SB, Ohki K, Reid RC, Bonhoeffer T, Hübener M.
Homeostatic regulation of eye-specific responses in visual cortex during ocular dominance plasticity.
Neuron. 2007 Jun 21;54(6):961-72.
PubMed.
Niell CM, Stryker MP.
Modulation of visual responses by behavioral state in mouse visual cortex.
Neuron. 2010 Feb 25;65(4):472-9.
PubMed.
Sale A, Maya Vetencourt JF, Medini P, Cenni MC, Baroncelli L, De Pasquale R, Maffei L.
Environmental enrichment in adulthood promotes amblyopia recovery through a reduction of intracortical inhibition.
Nat Neurosci. 2007 Jun;10(6):679-81. Epub 2007 Apr 29
PubMed.
These findings are novel and provide further support for the importance of physical activity in brain plasticity. Specifically, Lunghi and Sale demonstrated that intermittent exercise of moderate intensity over a two-hour period enhanced short-term plasticity of the adult visual cortex. This is notable because it demonstrates the breadth of plasticity that can be induced by physical activity. The majority of previous studies have focused on ascertaining the benefit of physical activity on cognitive and motor plasticity. Moreover, this evidence of brain plasticity was demonstrated in adults—individuals well beyond the critical period of developmental plasticity. Thus, the notion that neuroplastic potential remains throughout the lifespan is supported by this study. In the future, it would be interesting to see if physical activity elicits similar enhancements in plasticity among those with pre-existing visual impairments.
Comments
Massachusetts General Hospital, Harvard Medical School
The ability to stimulate plasticity in the adult brain would provide a means to enable patient recovery from a variety of insults and conditions including stroke, amblyopia, and neurodegenerative disease. In this recent correspondence, Lunghi and Sale report that intermittent exercise by human subjects during a brief visual system challenge can significantly enhance a shift in perception that occurs with visual challenge alone. When presented with incongruent images to each eye, subjects report alternating perception of each of the two images, a phenomenon termed binocular rivalry. Following a brief period of monocular deprivation (MD), subjects report increased perception of images presented to the deprived eye. Lunghi and Sale report that this shift is more pronounced if subjects perform intermittent exercise during the MD period. Paralleling studies in experimental models in which environmental modification can stimulate visual system plasticity in the adult brain (He et al., 2007; Sale et al., 2007), these data suggest that exercise can enhance plasticity in the human brain in ways that could be harnessed to overcome deficits produced by disease.
This study raises a number of interesting issues. The authors compare the shifts in perception that subjects exhibit during binocular rivalry to plastic shifts in ocular dominance (OD) described in experimental animals following MD. OD, the relative strength of responsiveness of the visual cortex to input from each eye, is most flexible during a critical period of postnatal development, though a number of different manipulations can greatly enhance this plasticity in adulthood (reviewed in Hubener and Bonhoeffer, 2014). However, shifts in perception of binocular rivalry occur much more quickly than do OD plasticity shifts (Gordon and Stryker, 1996) and more quickly than homeostatic changes thought to contribute to OD plasticity in experimental models (Keck et al., 2013; Mrsic-Flogel et al., 2007). Whether the more rapid change in binocular rivalry is due to plasticity at a smaller, more malleable set of synapses, or it represents a different kind of adaptation, is an important question when considering how these findings relate to plasticity in the brain more broadly. Though enhanced with exercise, the shift in binocular rivalry can occur in the absence of exercise, raising the possibility that this adaptive ability of the cortex may be present and constant throughout life and less analogous to other forms of cortical plasticity that are more difficult to engage in adulthood.
How does exercise modulate the plasticity of binocular rivalry? In mice, running has been demonstrated to enhance primary visual cortical responses to visual input (Niell and Stryker, 2010), at least in part through the modulation of inhibitory circuitry (Fu et al., 2014). In the current study, exercise may induce a more robust shift in rivalry post-challenge by increasing the magnitude of visual cortical responses during MD. Whether this effect is short-lived and/or represents a type of plastic change that could be harnessed to rewire damaged or dysfunctional cortex is an important question. Along with a better understanding of the circuit-level basis for the phenomenon described in this study, future studies should provide a clearer picture of the potential for exercise to enhance adult plasticity more broadly.
References:
Fu Y, Tucciarone JM, Espinosa JS, Sheng N, Darcy DP, Nicoll RA, Huang ZJ, Stryker MP. A cortical circuit for gain control by behavioral state. Cell. 2014 Mar 13;156(6):1139-52. PubMed.
Gordon JA, Stryker MP. Experience-dependent plasticity of binocular responses in the primary visual cortex of the mouse. J Neurosci. 1996 May 15;16(10):3274-86. PubMed.
He HY, Ray B, Dennis K, Quinlan EM. Experience-dependent recovery of vision following chronic deprivation amblyopia. Nat Neurosci. 2007 Sep;10(9):1134-6. Epub 2007 Aug 12 PubMed.
Hübener M, Bonhoeffer T. Neuronal plasticity: beyond the critical period. Cell. 2014 Nov 6;159(4):727-37. PubMed.
Keck T, Keller GB, Jacobsen RI, Eysel UT, Bonhoeffer T, Hübener M. Synaptic scaling and homeostatic plasticity in the mouse visual cortex in vivo. Neuron. 2013 Oct 16;80(2):327-34. PubMed.
Mrsic-Flogel TD, Hofer SB, Ohki K, Reid RC, Bonhoeffer T, Hübener M. Homeostatic regulation of eye-specific responses in visual cortex during ocular dominance plasticity. Neuron. 2007 Jun 21;54(6):961-72. PubMed.
Niell CM, Stryker MP. Modulation of visual responses by behavioral state in mouse visual cortex. Neuron. 2010 Feb 25;65(4):472-9. PubMed.
Sale A, Maya Vetencourt JF, Medini P, Cenni MC, Baroncelli L, De Pasquale R, Maffei L. Environmental enrichment in adulthood promotes amblyopia recovery through a reduction of intracortical inhibition. Nat Neurosci. 2007 Jun;10(6):679-81. Epub 2007 Apr 29 PubMed.
University of British Columbia
These findings are novel and provide further support for the importance of physical activity in brain plasticity. Specifically, Lunghi and Sale demonstrated that intermittent exercise of moderate intensity over a two-hour period enhanced short-term plasticity of the adult visual cortex. This is notable because it demonstrates the breadth of plasticity that can be induced by physical activity. The majority of previous studies have focused on ascertaining the benefit of physical activity on cognitive and motor plasticity. Moreover, this evidence of brain plasticity was demonstrated in adults—individuals well beyond the critical period of developmental plasticity. Thus, the notion that neuroplastic potential remains throughout the lifespan is supported by this study. In the future, it would be interesting to see if physical activity elicits similar enhancements in plasticity among those with pre-existing visual impairments.
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