Dr Dempsey-Jones of University College London recently visited Charterhouse to give a talk to pupils in the Perception Society. The article below was written by Adelina Dan.
We often perceive “feeling” as an act dependent on the body. It feels linked, it feels natural, but it fails to answer some interesting phenomena. Dr Dempsey-Jones looks at how we can enhance our sense of touch through exposure and training, as well as how brain mapping is possible with the help of some relatively simple exercises on patients’ part. In this week’s Perception lecture, we learned how touch can be accessible for all.
Both recent and old amputees have had sensation in limbs which they no longer had, an experience known as phantom sensations. Thus, the necessity of having a body in order to achieve a full range of movement and feeling begins to be questioned, especially when regarded in light of possible technological developments. But first, before we think of the future, let us consider what we already know.
Our nervous system is made up of the brain and the spinal cord, which combine to form the central nervous system; alongside this, the sensory and motor nerves form the peripheral nervous system. Try and perceive the brain and spinal cord as the hubs, while the sensory and motor nerves are the chords which stretch out to provide access to all areas of the body. At the finger level, for example, environmental stimuli such as heat are acknowledged by sensory nerves, then sending impulses about what is happening in our environment to the brain via the spinal cord. The brain sends information back to the motor nerves, which help us perform actions- in the case of our fingers touching a hot pan, our brain would naturally tell us to move our fingers away. The peripheral nervous system, different sensory nerve fibres respond to different things, producing different chemical responses determining how sensations are interpreted.
Where the story becomes even more fascinating, however, is when we look at the organisation of the brain; interestingly, there are segments distinguished by sulci (groove in central cortex) representing each part of the body. Whilst these don’t represent the size of the body part, they represent how many touch receptors they each have. As seen in the diagram below by Penfield and Rasmussen, areas such as the lips have very good touch perception when compared to the trunk or shoulder.
Whilst working with patients suffering of epilepsy , Dr Penfield looked to localise the cause of the problem and remove the corresponding area of the brain; this later turned out to be revolutionarily known as intraoperative brain mapping. Patients were locally anaesthetised, but were kept awake during the open brain surgery: after the skull was opened, the surgeon would use fine electrodes to send localised electrical impulses on different areas of the brain, following up with questions to the patient as to what part of the body they felt affected. For example, if the surgeon touched the sulcus responsible for nose touch perception, the patient would feel a slight tingle in their nose.
Dr Dempsey-Jones’ research involved mapping the hand map in very fine detail, using a 7 Tesla scanner with 1 mm precision. She asked her investigation participants to move one finger at a time, and assigned a colour to each one of them in order to distinguish patterns and irregularities:
Whilst this investigation helped to identify whether mapping was possible in non-amputees, there is a question left unanswered: do areas which correspond with lost limbs still show brain activity?
Researchers looked at whether amputees have a hand ‘map’- a defined, distinguished response in the cortex- by using FMRI, which takes pictures of the brain while it is active. It sees where blood flows, and where it changes from oxygenated to deoxygenated. Interestingly, there is activity seen even in people who only have a ‘phantom hand’. Although more sparse and dispersed, there is still clear cortex activity for amputees in the areas which are normally associated with hand touch perception.
The preservation of the hand map in amputees allows us to consider the possibility of associating touch perception with an artificial arm. Nathan Copeland (28), was the first paralysis patient to try a two-way feedback neural implant, which would allow him to control a prosthetic arm with simply his thought. To capture electrical signals from the brain, scientists have developed microelectrode arrays smaller than a square centimetre which, after being implanted in the brain on the area associated with hand movement, they record electrical activity, then translating the recorded information through a thin cable to the prosthetic arm. Similarly, in the robotic arm there are sensors which are sensitive to touch pressure, which sends impulses back to the sensory cortex in the brain. Whilst blindfolded, Nathan was able to determine which finger is prodding an external stimuli, proving the success of the prosthetic (Robotic arm video).
This is incredibly revolutionary for amputees and paralysis patients, offering the possibility of a successful future, as well as the prospect of further developing neuroplasticity research and discovering its applications. We are ever so grateful for being introduced to Dr Dempsey-Jones’ research, and being able to grasp the concept of an incredibly interesting and promising concept.
Further reading on giving a sense of touch to robots: