Measuring the detailed topography and neural correlates of attention in somatosensory cortex with high-resolution fMRI

Modern neuroimaging methods have made it possible to study many neuroscience questions in the human. By using functional magnetic resonance imaging (fMRI), for example, we can measure changes in the local blood flow that occurs with increased neural activity. This causes an increase in the signal intensity in the MR image in the part of brain that is being used. We can measure for example which parts of the brain are more active while subjects feel an object touch their index finger. One of the problems we have when studying the mechanism underlying our sense of touch is that the changes that occur in the human brain are relatively small. The visual cortex by comparison where information from they eyes is processed for 'seeing', covers an area many times the size. Until now, researchers have therefore concentrated on the visual brain in humans, and have had more limited success in studying the somatosensory cortex. In a collaboration between the Schools of Psychology and Physics at the University of Nottingham, we have started using some cutting-edge technology to measure responses to touch in the human brain.. By using a very high field magnetic resonance (MR) scanner developed by the world-class Physics group at the University of Nottingham we can detect signal changes in small brain areas much better. We can measure robust neural responses non-invasively with much higher spatial resolution than has previously been possible. The neuroscience questions in this proposal fit squarely into the remit of the BBSRC of understanding normal human function, but our proposed research also has a strong interdisciplinary component. Because imaging at very high field strengths requires a lot of technical expertise a collaborative link between researchers in neuroscience and physics is absolutely crucial. Specifically, we will use high-resolution fMRI to map carefully the detailed anatomy and function of the human somatosensory cortex by looking for an orderly map of the representation of the fingers in the brain. In pilot data we have collected during the last year we demonstrate that with very high (1mm3) resolution measurements we can indeed reveal a topographic map of the hand representation in the human brain. We also aim to map how the brain processes different frequencies of touch (for example an indentation compared to a tap). Animal models have shown that this involve different parts of the somatosensory system on the spatial scale of several millimetres. We will then study how attention modulates the perception of touch and how the responses in the brain that underlie these perceptions. While subjects are being scanned, we will ask them to attend to a specific part of the skin on their fingers. We will then test how paying attention changes the responses in the part of the brain that processes information from that region of the skin surface. From these measurements, we can then make inferences about how the brain integrates information across the different brain regions used in finger representation, and how attention acts to modulate these responses.

Alot is known about how attention improves visual perception but much less about our sense of touch, because it has been difficult to reliably map the fine topography of somatosensory cortex. Our research addresses how spatial and non-spatial attention modulates tactile perception. To this end, we will first use established experimental designs and analyses to topographically map the fingers in the human somatosensory cortex in individual subjects. We will measure the cortical mapping of the fingers at very high spatial resolution using functional magnetic resonance imaging (fMRI) at 7T. By using 1mm isotropic voxels in our fMRI experiments, we have already been able to reveal the fine-grained topographic map of the digit representation in human somatosensory cortex much better than any current studies. We will extend this mapping experiment to two other aspects of organization in somatosensory cortex that are on the spatial scale of several millimetres: clustering of neurons that prefer low or high flutter frequencies of somatosensory stimulation and the mapping of individual digits (from tip to base) onto cortex. We will then use high-resolution fMRI measurements to probe the attentional modulation of these somatosensory cortical responses. We will measure the cortical response to digit representations while subjects perform simple tactile tasks: target detection or search in temporal stream or spatial array of vibrotactile stimuli. Attention to tactile events will be (a) focused on one of the stimulated digits, (b) diverted from all digits, and (c) divided between two different digits. By using an event-related paradigm, we will be able to establish the temporal and spatial extent of the tactile attentional 'spotlight'. To identify whether non-spatial attention can specifically enhance responses from different receptor types in the skin, we will measure the responses to mixtures of low and high-frequency stimuli.