Learning and plasticity in the human brain

National Institute Of Mental Health

Investigators

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Abstract

The primary goals of this research are i) to establish how learning impacts the structure and function of the brain, and ii) to determine how learning can be modulated. 1) Impact of experience on representation of expert tools in the brain (NCT00001360) The idea that when we use a tool we incorporate it into the neural representation of our body (embodiment) has been a major inspiration for philosophy, science and engineering. While theoretically appealing, there is little direct evidence for tool embodiment at the neural level. Using functional magnetic resonance imaging (fMRI), we investigated whether expert tool users (London litter pickers) represent their expert tool more like a hand (embodiment) or less like a hand (differentiation), as compared to a group of tool novices. During fMRI scans, participants viewed videos depicting grasps performed by either a hand, litter picker or a non-expert grasping tool. We measured the patterns of response in brain regions known to represent hands and tools (occipitotemporal cortex and parietal cortex) and found differences in the representational structure of hands and tools between experts and novices. Contrary to the embodiment theory, we find that experts represent their own tool less like a hand, providing an important alternative framework to the prominent tool embodiment theory. 2) Modulating learning - Impact of prosthesis training on hand representations (NCT00001360) As described above, we found that expert tools become more differentiated from the representation of the hand (i.e. less embodied), and a similar result has been found for prosthetic limbs in amputees. However, the development of prosthetic devices emphasizes embodiment as the goal with the design and the control of devices becoming more biomimetic (mimicking the body). In this context it is notable that there are low rates of prosthetic hand usage and even complete device rejection are common in upper-limb amputee populations. If experience with a device does not lead to representing it more like a real body part, then maybe the quest to design artificial hands that look and act in the same way as the human body is misguided and may actually hinder usage. Here, we are investigating how different training regimens, and in particular intuitive (biomimetic) versus arbitrary control mechanisms, impact the representation of prosthetic and real hands. We are training able-bodied participants to use an artificial hand simulator, similar to a prosthesis, that can be strapped to the forearm and controlled via electromyographic (EMG) readings from the arm. Participants are trained with either a biomimetic control system (matching robotic hand movements to real hand movements) or an arbitrary control system (matching robotic hand movements to arbitrary real hand movements). We are measuring the impact of these different training regimens by collecting extensive behavioral and fMRI measures before and after training. Establishing the nature, degree and consequences of plasticity in the adult cortex provides important insights into the potential for rehabilitative brain therapies following injury or dysfunction in the nervous system.