Our ability to manipulate objects dexterously relies fundamentally on sensory signals originating from the hand. To restore motor function with upper-limb neuroprostheses requires that somatosensory feedback be provided to the tetraplegic patient or amputee. Given the complexity of state-of-the-art prosthetic limbs and, thus, the huge state space they can traverse, it is desirable to minimize the need for the patient to learn associations between events impinging on the limb and arbitrary sensations. Accordingly, we have developed approaches to intuitively convey sensory information that is critical for object manipulation—information about contact location, pressure, and timing—through intracortical microstimulation of primary somatosensory cortex. In experiments with nonhuman primates, we show that we can elicit percepts that are projected to a localized patch of skin and that track the pressure exerted on the skin. In a real-time application, we demonstrate that animals can perform a tactile discrimination task equally well whether mechanical stimuli are delivered to their native fingers or to a prosthetic one. Finally, we propose that the timing of contact events can be signaled through phasic intracortical microstimulation at the onset and offset of object contact that mimics the ubiquitous on and off responses observed in primary somatosensory cortex to complement slowly varying pressure-related feedback. We anticipate that the proposed biomimetic feedback will considerably increase the dexterity and embodiment of upper-limb neuroprostheses and will constitute an important step in restoring touch to individuals who have lost it.Although it has been shown that percepts can be elicited with intracortical microstimulation (ICMS) of primary somatosensory cortex (S1) (
1–
7), a major challenge in developing approaches to convey sensory feedback using ICMS in animal models is to assay the evoked sensations (
8). One way to circumvent this obstacle is to train animals to discriminate sensory stimuli along a dimension of interest, and then to assess whether the animals can perform the task when physical stimuli are replaced with ICMS (
2,
3). In this approach, ICMS regimes are designed to mimic the patterns of neuronal activation that encode the relevant sensory dimension. In the context of upper-limb neuroprostheses, contact location, pressure, and timing are three of the most basic cutaneous signals that mediate object grasping and manipulation (
9). In somatosensory cortex of intact primates, the neural coding of stimulus location (i.e., which parts of the hand are contacting the object) presumably relies on somatotopic organization: The population of activated neurons within the body representations in S1 (one each in areas 3a, 3b, 1, and 2) determines where on the body the sensation is projected (
10). We can attempt to convey information about contact location by targeting ICMS on populations of neurons with specific receptive field (RF) locations. The neural coding of contact pressure might rely on two mechanisms: (
i) as the pressure exerted on the skin increases, the neuronal population with RFs under the stimulus becomes more active, and (
ii) neurons with adjacent RFs will become activated so the size of the activated population will increase (
11). We might thus convey information about pressure by increasing the amplitude of ICMS—thereby increasing both the strength of activation of neurons near the electrodes and the size of the activated population (
12). The neural coding of contact timing—which signals when contact with an object is initiated and terminated—is thought to rely on the on and off responses produced in S1 neurons at the onset and offset of contact and lasting on the order of 50–100 ms (
13). These temporally precise responses are relatively insensitive to object properties (
14) and critical in guiding the dexterous manipulation of objects (
9). We might convey information about contact timing by delivering phasic ICMS at the onset and offset of object contact. Our experimental approach consists in mimicking natural patterns in the brain and assessing whether the animal spontaneously interprets these induced patterns correctly.
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