Two-point discrimination
Encyclopedia
Two-point discrimination is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination
and reflects how finely innervated an area of skin
is.
Two-point discrimination is a reliable and widely used technique for determining tactile gnosis
. It relies on the ability and/or willingness of the patient to subjectively report what s/he is feeling and should be completed with the patient’s eyes closed. In order to test for two-point discrimination, the therapist will use a special pair of calipers (or reshaped paperclip). The therapist will alternate (randomly) between touching the patient with one point or with two points on the area being tested (e.g. finger, arm, leg, toe). The patient will then be asked to report back what s/he felt (one or two points). The smallest distance between two points at which the patient can still distinguish as two separate stimuli and not one, is recorded. Each extremity should be tested and compared side to side for discrepancies.
The smallest and most dense sensory units are located in those areas that have the greatest somatosensory cortical representation. Normally, a person should be able to recognize two points separated by as little as 2-4 mm on the lip
s and finger
pads, 8-15 mm on the palms and 30-40 mm on the shins
or back (assuming the points are at the same dermatome
).
The posterior column-medial lemniscus pathway
is responsible for carrying information involving fine, discriminative touch. Therefore, upon damage to this pathway, two-point discrimination can be impaired.
Neurological examination
A neurological examination is the assessment of sensory neuron and motor responses, especially reflexes, to determine whether the nervous system is impaired...
and reflects how finely innervated an area of skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
is.
Two-point discrimination is a reliable and widely used technique for determining tactile gnosis
Gnosis
Gnosis is the common Greek noun for knowledge . In the context of the English language gnosis generally refers to the word's meaning within the spheres of Christian mysticism, Mystery religions and Gnosticism where it signifies 'spiritual knowledge' in the sense of mystical enlightenment.-Related...
. It relies on the ability and/or willingness of the patient to subjectively report what s/he is feeling and should be completed with the patient’s eyes closed. In order to test for two-point discrimination, the therapist will use a special pair of calipers (or reshaped paperclip). The therapist will alternate (randomly) between touching the patient with one point or with two points on the area being tested (e.g. finger, arm, leg, toe). The patient will then be asked to report back what s/he felt (one or two points). The smallest distance between two points at which the patient can still distinguish as two separate stimuli and not one, is recorded. Each extremity should be tested and compared side to side for discrepancies.
The smallest and most dense sensory units are located in those areas that have the greatest somatosensory cortical representation. Normally, a person should be able to recognize two points separated by as little as 2-4 mm on the lip
Lip
Lips are a visible body part at the mouth of humans and many animals. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech...
s and finger
Finger
A finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates....
pads, 8-15 mm on the palms and 30-40 mm on the shins
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
or back (assuming the points are at the same dermatome
Dermatome
Dermatome may refer to:*Dermatome , a surgical instrument used to produce thin slices of skin*Dermatome , an area of skin that is supplied by a single pair of dorsal roots*Dermatome...
).
The posterior column-medial lemniscus pathway
Posterior column-medial lemniscus pathway
The posterior column-medial lemniscus pathway is the sensory pathway responsible for transmitting fine touch, vibration and conscious proprioceptive information from the body to the cerebral cortex; as well as tactile pressure, barognosis, graphesthesia, stereognosis, recognition...
is responsible for carrying information involving fine, discriminative touch. Therefore, upon damage to this pathway, two-point discrimination can be impaired.