living without touch

Commonly recognized senses: vision, hearing, touch, taste, smell.
Proprioception, the sense of position and movement, is crucial for independence and mobility, yet often overlooked.
Lack of awareness of proprioception can be attributed to the absence of examples of people who have lost it.
Recent emergence of subjects who lost proprioception/ touch offers new opportunities for study.
Focus of the paper: investigation of movement management in the absence of peripheral feedback and implications for self-awareness.

Peripheral Nervous System (PNS): Comprises nerves outside the brain and spinal cord.
- Sensory nerves: responsible for transmitting impulses from peripheral organs to the central nervous system.
- Classification of nerve fibers:
  - Myelinated fibers (larger, faster conduction) vs. unmyelinated fibers (smaller, slower).
Receptors:
- Found in skin (cutaneous receptors) and muscles (muscle spindles and Golgi tendon organs responsive to stretch).
- Uneven distribution across the body; more receptors in hands than in back and buttocks.
- Notably, neck muscles house a significant amount of muscle spindles for fine control of movement.
Charles Bell's Contribution (1833):
- Identified joint position and movement sense as a sixth sense, crucial for balance and posture.
- Introduced concepts of unconscious motor schema and conscious body image.

Several patients reported between 1980-2000 with severe sensory peripheral neuropathies likely caused by autoimmune responses.
Case of I.W.:
- Suffered from viral infections leading to loss of touch and proprioception from the collarbone down.
- Retained vestibular sense for head movement.
Case of G.L.:
- Similar background but loss begins at the mouth level, affecting neck muscle control.
- Essential movements for speaking and facial expressions severely impaired.
Both cases demonstrate how loss of sensory feedback affects motor control.

Neither subject retains normal touch or proprioceptive sensations below their loss levels.
I.W. experiences:
- Describes lack of tactile sensation as frightening; requires intense concentration to move accurately.
- Significant progress in rehabilitation with mental effort; focused on independence despite limitations.
G.L. experiences:
- Developed adaptive strategies for speech and eating despite severe impairments, initially had to learn manual adjustments.
- Tasks involved conscious planning rather than unconscious body schema.

Differences in Motor Skills:
- I.W. displays better walking abilities linked to intact neck proprioception.
- G.L.'s lack of information from neck muscles hinders her balance and movement control.
Successful rehabilitation depends on patient motivation, prior learning, and existing sensory feedback.

Deafferented individuals adapted by altering types of spatial frames they use (egocentric vs. exocentric).
Egocentric frame relies on body position; exocentric frame relies on environmental context.
Studies indicate impairments in egocentric spatial awareness and suggest reliance on visual inputs.

Performance in reaching and pointing tasks affected; reliance on visual feedback rather than proprioceptive input.
Subjects demonstrate varying capabilities between morphokinesis (shape-based movement) and topokinesis (space-based movement).
I.W. and G.L. differ in their cognitive processing and adaptation strategies, leveraging visual cues differently.

I.W. maintains a confident body image based on long-standing neural mappings, despite neurological changes.
G.L. perceives her body in terms of mechanical commands emphasizing her psychological adaptation to disability.
Both exhibit a greater reliance on visual feedback for their body image and awareness in absence of proprioceptive input.
These changes impact their interactions with the external environment and their perception of personal space.

The unique cases illustrate the roles of touch and proprioceptive feedback in movement and perception.
Future research can explore recovery, adaptation, and the possibility of visual proprioception compensating for physical sensory loss.
Individuality in adaptation processes emphasizes the importance of tailored rehabilitation strategies.