The Tactile Helmet is designed to augment a wearer's senses with long-range touch. Tactile specialist animals e.g. rats are capable of rapidly acquiring detailed environmental information from their whiskers using task-sensitive strategies. Providing similar information about the environment, in tactile form, to a human operator could prove invaluable for search and rescue, or partially-sighted people. Key aspects of the Tactile Helmet are sensory augmentation, and active sensing. A haptic display is used to provide users with ultrasonic range information. This can be interpreted in addition to visual or auditory information. Active sensing systems are "purposive, information-seeking sensory systems, involving task-specific control of sensory apparatus" [1]. The integration of an accelerometer allows the device to actively gate the delivery of sensory information to the user, depending on their movement. We describe the hardware, sensory transduction and characterisation of the Tactile Helmet device, outlining use cases and benefits of the system.
Dopaminergic (DA) neurons respond to stimuli in a wide range of modalities, although the origin of the afferent sensory signals has only recently begun to emerge. In the case of vision, an important source of short-latency sensory information seems to be the midbrain superior colliculus (SC). However, longer-latency responses have been identified that are less compatible with the primitive perceptual capacities of the colliculus. Rather, they seem more in keeping with the processing capabilities of the cortex. Given that there are robust projections from the cortex to the SC, we examined whether cortical information could reach DA neurons via a relay in the colliculus. The somatosensory barrel cortex was stimulated electrically in the anesthetized rat with either single pulses or pulse trains. Although single pulses produced small phasic activations in the colliculus, they did not elicit responses in the majority of DA neurons. However, after disinhibitory intracollicular injections of the GABAA antagonist bicuculline, collicular responses were substantially enhanced and previously unresponsive DA neurons now exhibited phasic excitations or inhibitions. Pulse trains applied to the cortex led to phasic changes (excitations to inhibitions) in the activity of DA neurons at baseline. These were blocked or attenuated by intracollicular administration of the GABAA agonist muscimol. Taken together, the results indicate that the cortex can communicate with DA neurons via a relay in the SC. As a consequence, DA neuronal activity reflecting the unexpected occurrence of salient events and that signaling more complex stimulus properties may have a common origin.
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