# Prosthesis Embodiment in Lower Extremity Limb Loss: A Narrative Review
## 4 Results
### TIME and C-FINE Devices  
Technologies such as TIME (Transverse Intrafascicular Multichannel Electrode) and C-FINE (Composite Flat Interface Nerve Electrodes) directly interface with peripheral nerves to provide both cutaneous and proprioceptive sensory feedback. By directly interfacing with the nerve, a more natural sensation can be achieved, and unlike many non-invasive approaches, extensive training is not required. These technologies allow amputees to regain sensations reminiscent of those of a biological limb, significantly improving their ability to control, interact with, and embody the prosthesis. TIME works by being transversely inserted into the peripheral nerve, enabling it to selectively activate subsets of axons within individual nerve fascicles. This design allows for highly precise stimulation at both the intrafascicular and interfascicular levels for tasks requiring targeted cutaneous sensory perception. [PERSON] et al. demonstrated in [58] the effectiveness of TIME electrodes in the selective activation of target muscles. After insertion, the device is connected to a custom neuroprosthetic system. This custom-designed prosthesis includes a sensorized foot insole. Signals from the insole, an encoder, and TIME electrodes are linked to re-establish cutaneous sensory feedback similar to that of a normal limb [59]. Furthermore, in [27], [PERSON] et al. showed that the subjects were able to recognize the degree of flexion of the knee at four different angles, as well as the approximate magnitudes and location of the forces exerted. When neural stimulation was removed, the subjects were unable to determine these quantities. In contrast, C-FINE devices wrap around larger nerves, such as the sciatic nerve. The rectangular cuff-like shape of the C-FINE device applies light pressure to the nerve, deforming it into a flatter geometry. This deformation helps to align the nerve fascicles more closely with the electrodes embedded in the cuff, improving the contact and stimulation efficiency [60]. C-FINE can be used in place of TIME devices in cases where less surgical intervention is desired or to complement them when cutaneous sensory coverage is needed for broader regions of the limb. Using high-density nerve cuffs, C-FINE systems provide consistent cutaneous sensory feedback and allow amputees to regain a natural sensation without the need for precise targeting that TIME electrodes offer. Table 2 from [43] provides a summary of the \"feelings\" that can be generated by varying the stimulus pulse. TIME and C-FINE are complementary approaches that can be used together. [PERSON] et al. built a model of how the sciatic nerve reacts to stimulation from TIME and C-FINE devices in [61]. Based on the simulations, a combination of TIME and C-FINE devices was best in terms of the number of fascicles that can be selectively stimulated. Both TIME and C-FINE devices reduce phantom limb pain for users [43]. For C-FINE devices, subjects felt that the location of the phantom big toe was correlated with the prosthesis [43], suggesting that the subject began to embody the device. Ref. [59] demonstrated that TIME patients reported reduced phantom limb pain with nerve stimulation, as quantified by the Neuropathic Pain Symptom Inventory, compared to without nerve stimulation. In addition to reducing phantom pain, TIME and C-FINE devices significantly improve functional outcomes for lower limb amputees, though it should be noted that these studies were carried out over small sample sizes. With TIME devices, ref. [59] showed that users were able to walk faster due to improved confidence and embodiment as a result of having restored cutaneous sensations. The link between embodiment and improved functional outcomes was demonstrated through a split-focus activity that involved identifying auditory cues while walking [59]. Finally, the speed was increased despite a decrease in energy expenditure and oxygen uptake. This means that the subject's walking gait and posture became more efficient [59].