Final answer:
The least sensitive areas to touch based on two-point discrimination are typically parts of the body with fewer sensory endings, such as the back, thighs, or calves. This contrasts with highly sensitive areas like the fingertips, which have a denser distribution of sensory receptors and a smaller two-point discrimination threshold.
Step-by-step explanation:
The areas of the body that are least sensitive to touch are generally those that have a lower density of sensory endings and larger receptive fields. Based on two-point discrimination tests, which measure the ability to perceive one versus two simultaneous touch points, areas like the back, thighs, or calves often display less sensitivity compared to areas with higher tactile acuity like the fingertips. The two-point discrimination test is a standard method to assess this aspect of somatosensory function.
During the test, specialized tools like calipers or forceps are used to touch the skin at two closely positioned points. The subject, with their eyes closed, must indicate whether they feel one or two separate points. The minimum distance at which two points are perceived as distinct can vary significantly between different body regions, with the fingertips often having the smallest distance and thus the highest sensory resolution.