Question

A demonstration in which the finger of a blindfolded student was used to tap the nose of a third student with the blindfolded student’s index finger. At the same time, the first student tapped the nose of the blindfolded student so that the taps on the two noses were synchronous. What was the purpose of this demonstration? How did this relate to the phenomenon of “phantom limbs”? What is Ramachandran’s “mirror box”? What does all of this tell us about the permanence, or lack thereof, the brain’s representation of the body? How does this relate to the discussion of somatovisual neurons in monkey parietal cortex and tool use?

Answer 1

The present demonstration exemplifies the working of the phantom limb hypothesis and it shows the role of sensory motor neural pathways in behaviour. In this case, if the synchronic taps on the nose experienced by the blindfolded person were repeatedly paired with the taps on the nose of the third person using the blindfolded Participant’s finger, then a case could emerge in the subsequent trials when the blindfolded person may experience the taps on his/her own nose when only his finger is the one that is used to create the taps on the other person’s nose without actual stimulation of his/her own nose. What this study indicates is that the mind and the body function within a feedback loop which is mediated by a network of sensory-motor nerves. Such a process operates within the neurological condition known as ‘phantom limbs’.

Phantom limbs is defined as a psychosomatic syndrome which is marked by the ability to feel sensations, often of pain in a parts of the body that have been amputated or damaged. For instance, persons who have had their limbs removed or amputated for some reason feel that the missing limb continues to be present in the body and it is still performing its normal functions. It has been found that the brain continues to receive signals from the nerve endings that originally supplied signals to and from the missing limb. The vortex of the brain which is the seat of executive functions in the human body undergoes a reconstitution in a way and it gradually rearranges sensory information to adjust to the changes in the body. This gap produced by rearrangement causes a confusion in the interpretation of signals thereby creating false perceptions about the continued existence of the lost body part.

While it may seem that this continued sensation may be harmless, often people with phantom sensations report sharp pain, tingling sensation, and cramps and numbness. This interferes with their day-to -day coping mechanisms and therefore requires medical intervention. It was with this view that Vilayanur S. Ramachandran invented the ‘mirror box’ to help alleviate phantom limb pain.

The mirror box is an instrument with two mirrors in the centre facing each other and the patient places the functional limb on one side, and the residual ‘phantom’ limb on the side of the other mirror.the patient is then instructed to look into the mirror on the side of the functioning limb and make ‘mirror symmetric’ movements such that the reflected image of the moving limb creates perceptions of the parallel( yet absent)movement of the phantom limb as well. Thus, the brain is tricked into seeing two complete limbs. Through the use of such artificial visual feedback, the patient is led towards unfreezing the phantom limb from painful positions. The mirror box therapy has been found to be an effective intervention for motor recovery.

Beyond its practical implications, the given demonstration testifies to the powerful feedback network within nervous system and both the sensations of nose tapping and the working of the mirror box indicate towards the enduring or the permanent nature of our mental representation about our own body. The continued sensory feedback experienced by the patients of the phantom limb can be explained by the process of Hebbian learning according to which the feedback such as about tingling sensations, or pain, stamped itself into the brain circuits such that even when the limb was no longer present or it was paralysed, the brain had learned that the limb was paralysed thereby making it difficult for the patient to move the limb.

Thus, the brain cortex is a seat of complex mental and behavioural processes. Experimental studies on the sensory motor coordination in monkeys have shown similar outcomes. For instance, in the study of eye-hand coordination in the rhesus monkeys using manipulation of different tools, it was found that a group of neurons related to hand movements exist in the posterior parietal cortex. The monkeys were trained to manipulate objects by their hands in the light and then in the dark. The study reported that not only were some neurons innervated by the hand movements but that majority of the neurons( 69%) were more active under the visual stimulation of light. Thus, the hand movement related neurons of the parietal cortex are concerned with the visual information which guides the hand movement.

Thus, to conclude all these instances, the demonstration, the mirror box and the study of the corticol neurons of the monkeys point towards a the prevalence of an enduring mind-body connections which help human and other species manipulate objects in their environment and learn to adapt.