Characterizing Brain Cortical Plasticity and Network Dynamics Across the Age-Span in Health and Disease with TMS-EEG and TMS-fMRI

Berenson-Allen Center for Noninvasive Brain Stimulation, Division of Cognitive Neurology, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.
Brain Topography (Impact Factor: 3.47). 08/2011; 24(3-4):302-15. DOI: 10.1007/s10548-011-0196-8
Source: PubMed


Brain plasticity can be conceptualized as nature's invention to overcome limitations of the genome and adapt to a rapidly changing environment. As such, plasticity is an intrinsic property of the brain across the lifespan. However, mechanisms of plasticity may vary with age. The combination of transcranial magnetic stimulation (TMS) with electroencephalography (EEG) or functional magnetic resonance imaging (fMRI) enables clinicians and researchers to directly study local and network cortical plasticity, in humans in vivo, and characterize their changes across the age-span. Parallel, translational studies in animals can provide mechanistic insights. Here, we argue that, for each individual, the efficiency of neuronal plasticity declines throughout the age-span and may do so more or less prominently depending on variable 'starting-points' and different 'slopes of change' defined by genetic, biological, and environmental factors. Furthermore, aberrant, excessive, insufficient, or mistimed plasticity may represent the proximal pathogenic cause of neurodevelopmental and neurodegenerative disorders such as autism spectrum disorders or Alzheimer's disease.

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    • "During the training, Growing When Required networks (Marsland et al., 2002) dynamically change their topological structure through competitive Hebbian learning (Martinetz, 1993) to incrementally match the input space. The learning process is built upon input-driven synaptic plasticity (Pascual-Leone et al., 2011) and habituation (Thompson and Spencer, 1966). Clustered neuronal activation trajectories from the parallel pathways are subsequently integrated to generate prototype neurons representing action dynamics in the joint pose-motion domain, resembling the neural integration of multi-cue action features in the visual cortex (Beauchamp et al., 2003). "
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    ABSTRACT: The visual recognition of complex, articulated human movements is fundamental for a wide range of artificial systems oriented toward human-robot communication, action classification, and action-driven perception. These challenging tasks may generally involve the processing of a huge amount of visual information and learning-based mechanisms for generalizing a set of training actions and classifying new samples. To operate in natural environments, a crucial property is the efficient and robust recognition of actions, also under noisy conditions caused by, for instance, systematic sensor errors and temporarily occluded persons. Studies of the mammalian visual system and its outperforming ability to process biological motion information suggest separate neural pathways for the distinct processing of pose and motion features at multiple levels and the subsequent integration of these visual cues for action perception. We present a neurobiologically-motivated approach to achieve noise-tolerant action recognition in real time. Our model consists of self-organizing Growing When Required (GWR) networks that obtain progressively generalized representations of sensory inputs and learn inherent spatio-temporal dependencies. During the training, the GWR networks dynamically change their topological structure to better match the input space. We first extract pose and motion features from video sequences and then cluster actions in terms of prototypical pose-motion trajectories. Multi-cue trajectories from matching action frames are subsequently combined to provide action dynamics in the joint feature space. Reported experiments show that our approach outperforms previous results on a dataset of full-body actions captured with a depth sensor, and ranks among the best results for a public benchmark of domestic daily actions.
    Frontiers in Neurorobotics 06/2015; 1(9 3). DOI:10.3389/fnbot.2015.00003
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    • "Sensory input from one side is mainly processed on the contralateral side of the brain along crossed pathway [1] [2]. Nevertheless, the sensory representation of both pathways will undergo remapping to respond to the brain injury, such as ischemic stroke [3]. Tissue lesion occurs within minutes up to hours after stroke, but functional recovery continues for weeks and months after the initial injury. "
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    ABSTRACT: Stroke could result in both structural and functional impairments. Sensory remapping is believed to play a special role in cortical plasticity, which contributes to the recovery after ischemic stroke. Previous studies using imaging and electrophysiological methods have found that sensory representations after stroke can remap not only to the surrounding areas, but also to remote areas. Based on a rodent photothrombotic stroke model using optical intrinsic signal (OIS) imaging, the present study attempts to investigate the remapping of sensory representation in contralesional cortex to ipsilesional hindlimb stimulation. Quantitative analysis revealed an overall expansion of hindlimb representation in contralesional cortex after stroke. Moreover, results indicated that hindlimb representation became less correlated to different stimulation intensity in contrast to the previous positive correlation before stroke. We speculate that diaschisis in the acute stage of stroke might account for such a change in contralesional sensory representation.
    2015 7th International IEEE/EMBS Conference on Neural Engineering (NER), Montpellier; 04/2015
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    • "Neuroplasticity can be conceptualized as an intrinsic property of the brain that enables modification of function and structure in response to environmental demands, via the strengthening, weakening, pruning, or addition of synaptic connections, and by promoting neurogenesis (Pascual-Leone et al., 2011). There is presynaptically-mediated short-term plasticity lasting hundreds of milliseconds to a few minutes (e.g., posttetanic potentiation), and postsynaptically-mediated long-term plasticity (potentiation or depression), lasting minutes to months (Nicholls et al., 2011; Lüscher and Malenka, 2012; Regehr, 2012). "
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    ABSTRACT: Neuroplasticity can be conceptualized as an intrinsic property of the brain that enables modification of function and structure in response to environmental demands. Neuroplastic strengthening of synapses is believed to serve as a critical mechanism underlying learning, memory, and other cognitive functions. Ex vivo work investigating neuroplasticity has been done on hippocampal slices using high frequency stimulation. However, in vivo neuroplasticity in humans has been difficult to demonstrate. Recently, a long-term potentiation-like phenomenon, a form of neuroplastic change, was identified in young adults by differences in visual evoked potentials (VEPs) that were measured before and after tetanic visual stimulation (TVS). The current study investigated whether neuroplastic changes in the visual pathway can persist in older adults. Seventeen healthy subjects, 65 years and older, were recruited from the community. Subjects had a mean age of 77.4 years, mean education of 17 years, mean MMSE of 29.1, and demonstrated normal performance on neuropsychological tests. 1Hz checkerboard stimulation, presented randomly to the right or left visual hemi-field, was followed by two minutes of 9Hz stimulation (TVS) to one hemi-field. After two minutes of rest, 1Hz stimulation was repeated. Temporospatial principal component analysis was used to identify the N1b component of the VEPs, at lateral occipital locations, in response to 1Hz stimulation pre- and post-TVS. Results showed that the amplitude of factors representing the early and late N1b component was substantially larger after tetanic stimulation. These findings indicate that high frequency visual stimulation can enhance the N1b in cognitively high functioning old adults, suggesting that neuroplastic changes in visual pathways can continue into late life. Future studies are needed to determine the extent to which this marker of neuroplasticity is sustained over a longer period of time, and is influenced by age, cognitive status, and neurodegenerative disease. Copyright © 2015. Published by Elsevier Inc.
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