Learning and plasticity in the human brain

National Institute Of Mental Health

Investigators

Linked publications & trials

Abstract

The primary goals of this research are i) to establish how learning and experience impact the structure and function of the brain, and ii) to determine how learning and plasticity can be modulated. There are two main areas of ongoing research: 1) How does the cortical hand representation change following amputation? Sensorimotor experiences throughout our lifespan are thought to shape the neural representation of the body. What happens to the adult brain when it loses a key source of input, for example, following the amputation of an arm? We longitudinally investigated the stability of the cortical hand representation, before and after elective hand amputation. Two patients underwent functional brain imaging twice pre-amputation and at two separate time-points following amputation: 3 months and 6 months. Additionally, we scanned 15 age-matched able-bodied control participants across the same timescale (60 scans in total). Using mapping of digit topography, representational similarity analysis and decoding over time, we show a remarkably consistent inter-digit representational structure of the pre-amputation hand and the post-amputation phantom (missing) hand. Overall, this work provides the first pre- and post-amputation longitudinal evidence for preserved representation of the phantom (missing) hand following amputation. Such evidence is critical for thinking about the development of brain computer interfaces (BCI) and prosthetic devices. 2) Modulating learning - Impact of prosthesis training on hand representations (NCT00001360) In prior work, we found that expert tools become more differentiated from the representation of the hand (i.e. less embodied). 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. In this study, we investigated how different training regimens, and in particular intuitive (biomimetic) versus arbitrary control mechanisms, impact the representation of prosthetic (bionic) and real hands. We trained 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 forearm. Participants were 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). For both trained groups, training improved bionic limb control, reduced cognitive reliance, and increased embodiment over the bionic hand. Biomimetic users had more intuitive and faster control early in training. Arbitrary users matched biomimetic performance later in training. Further, arbitrary users showed increased generalization to a novel control strategy. Collectively, our findings suggest that biomimetic and arbitrary control strategies provide different benefits. The optimal strategy is likely not strictly biomimetic, but rather a flexible strategy within the biomimetic to arbitrary spectrum, depending on the user, available training opportunities and user requirements. In addition to the behavioral data, we also collected functional MRI measures before and after training. In ongoing analyses we are investigating how visual and motor representations of the real and bionic hand change over the course of 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.