Funds for this proposal will be used to train the applicant to perform combined psychophysical studies of humans and neurophysiological studies of non-human primates able to perform complex tactile discrimination tasks. The experiments address two fundamental questions related to somatosensory cortical plasticity. First, we will determine if cortical plasticity following tactile training alters related perceptual abilities, by describing if plasticity induced during one task alters ability in performing other tasks. While many studies have shown that the cortex is plastic, it is unknown how this plasticity is related to perception in general. Second, we will investigate the mechanisms by which attention induces plasticity. It is well known that attending to stimuli is important for learning to occur. Previous studies have shown that non-human primates attending to simultaneous stimulation of multiple digits develop novel multi-digit representations in primary somatosensory cortex, area 3b (SI, 3b). Furthermore, it is known that selective attention changes somatosensory neurons'firing rate and the degree of synchronous firing between neurons. We test here whether attention causes plasticity via changes in synchrony and putative Hebbian mechanisms. To address the first question of the perceptual relevance of this plasticity, in Aim 1, we will determine what happens to single and multi-digit tactile spatial-perception as a result of training humans with multi-digit stimuli. We hypothesize that multi-digit tactile spatial acuity will increase at the expense of single digit tactile spatial acuity. The results will provide a better understanding of the mechanisms of learning. It will also help describe how symptoms of focal dystonia are related to tactile input, and how to direct plasticity during rehabilitation. We also address how attention acts upon mechanisms of plasticity and how regions that presumably control attentional signals are altered during learning.
In aim 2 we will investigate the role of attention on cortical plasticity, and test a potential mechanism that drives plasticity: is plasticity is related to attentionally- induced cortical synchrony? In aim 2a we will record from cell pairs in SI, 3b while an animal attends to a multi-digit tactile task or a visual task while receiving the same tactile stimulation. We predict that cell pairs will exhibit more synchrony during the tactile task and this will correspond to greater receptive field expansion. We also predict that animals attending to a tactile stimulus will show greater SI, 3b map plasticity than animals attending to a visual task.
In aim 2 b, we will analyze data recorded simultaneously from the ventrolateral prefrontal cortex (vLPFC) while the animal learns the tactile task. This area is connected with somatosensory cortices, and is implicated in multisensory attentional mechanisms and tactile working memory. We predict that vLPFC activity will predict somatosensory plasticity and attentional synchrony.
This aim will therefore test a precise explanation as to why attention is necessary to induce/enhance plasticity. Such results would help us to better understand how cognitive states interact with brain processes that occur during learning.
We wish to understand how cortical plasticity following training on a tactile discrimination task influences tactile perception and how attention alters primary somatosensory responses to enhance plasticity. The specific type of plasticity we will study is implicated in focal dystonia;therefore understanding these mechanisms will guide future treatments of this disorder. In addition, by knowing exactly how attention alters brain structure we can describe mechanisms of sensorimotor skill development and learning to guide education and rehabilitation.