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The Motor and Sensory Cortex

The Motor and Sensory Cortex

We place no reliance
On virgin or pigeon
Our method is science
Our aim is Religion.

Aleister Crowley.

We owe much of our knowledge to this area of the brain from the famous work of Wilder Penfield.

Opening the cranium of conscious patients, he stimulated various areas of the brain to discover what responses would occur. These experiments that occurred before much of the current technology existed, might mean that the “Penfield Map” is not entirely accurate.

Ramachandran’s work with amputees experiencing “phantom limb” pains has contributed much of our understanding of how the motor and sensory cortex areas function.

For example, Ramachandran describes several patients who, having lost a lower leg or foot, will experience sensations there during orgasm or genital stimulation. Given the adjacency of the genital and foot/toes on the sensory cortex, this is understandable. Similarly, several patients had “remapped” the sensations of the phantom hand onto their cheek for similar reasons. Ramachandran goes on to hypothesize that this might account for some people’s sexual arousal with regards to “toes sucking”.

Penfield’s “homunculus” (little man) shows the extent to which the sensory areas are proportionally mapped out. The bigger the body part is demonstrating, the greater the area is represented on the sensory cortex.

The Motor Association Areas

Map of the body in the human brain. The cerebral cortex has been “inflated” to show the results more clearly. Movements of different body parts evoked activity in the primary motor cortex (left of the central sulcus, shown by the arrow) and primary somatosensory cortex (right of the central sulcus). The map also shows eye-movement activity in the frontal eye field and the parietal cortex. The map is a winner-take-all. Although different body parts activated overlapping areas of cortex, only the strongest activations are indicated. The map in the primary motor cortex contains two common complexities. First, the hand representation (red) is surrounded on three sides by a representation of the wrist. Second, there are two distinct hand representations possibly corresponding to areas 4a and 4p.
Image from: Michael Graziano

The primary motor area sends information to the larger motor association area. Similarly, the primary sensory area forwards the information to the larger sensory association area.

Damage to any of these areas can typically produce a deficit that will manifest on the opposite side of the body, owing to the contra-lateral control of the hemispheres. This is most commonly seen from the effects of a cerebral vascular accident (“stroke”)

For example, damage to the left parietal lobe may result in the person being unable to control their right arm/hand. If the damage is extensive, speech and language may be affected as well.

It has been suggested that “proprioception”, the ability to know where parts of the body are without visual confirmation, is located in the left parietal hemisphere. Patients with this area of damage will generally point to the incorrect part of the body when asked to locate another specific part:

“She could scarcely even sit up – her body ‘gave way’. Her face was oddly expressionless and slack, her jaw fell open, even her vocal posture was gone.

“Something awful’s hahappened, she mouthed, in a ghostly flat voice. “I can’t feel my body. I feel weird – disembodied.”


This was an amazing thing to hear, confounded, confounding. “Disembodied” – was she crazy? But what of her physical state then? The collapse of tone and muscle posture, from top to toe; the wandering of her hands, which she seemed unaware of; the flailing and overshooting, as if she were receiving no information from the periphery, as if the control loops for tone and movement had catastrophically broken down.


“What I must do then,” she said slowly, “is use vision, use my eyes, in every situation where I used – what do you call it? – proprioception before. I’ve already noticed,” she added, musingly, “that I may ‘lose’ my arms. I think they’re in one place, and I find that they’re in another. This “proprioception” is like the eyes of the body, the way the body sees itself. And if it goes, as it’s gone with me, it’s like the body’s blind. My body can’t “see” itself if it’s lost it’s eyes, right? So, I have to watch it – be it’s eyes. Right?”

Oliver Sacks – The Man Who Mistook His Wife for a Hat. P45-46.

Whilst the total loss of proprioception is comparatively rare, owing to the overall number of structures involved, certain meditative/trance states will induce this rapidly. For trance ratification, loss of bodily awareness is a good facilitor of trance and is easily induced by the novice. Sensory deprivation/floatation tanks will induce this very rapidly, whilst leaving consciousness unimpaired. Combining sensory deprivation along with trance/deep relaxation/meditation can produce some very profound states indeed. To this end, many psychonauts report that ketamine produces the same.

Circuit VIII is triggered by Ketamine, a neuro-chemical researched by Dr. John Lilly, which is also (according to a widespread but unconfirmed rumour) given to astronauts to prepare them for space. High doses of LSD also produce some circuit VIII quantum awareness.

Robert Anton Wilson. Cosmic Trigger.


[The] Eighth [Circuit]: Use Neuro-atomic technology to create universe and black wholes.

Dr. Timothy Leary.

Artificial loss of proprioception can enable the psychonaut to achieve “out of body experiences”, floating and/or the experience of levitation, as often claimed by people practicing TM and other meditational practices:

The student sits cross-legged on a large and thick cushion. He inhales slowly and for a long time, just as if he wanted to fill his body with air. Then, holding his breath, he jumps up with legs crossed, without using his hands and falls back on his cushion, still remaining in the same position. He repeats that exercise a number of times during each period of practice. Some lamas succeed in jumping very high in that way. Some women train themselves in the same manner.


As one can easily believe the object of this exercise is not acrobatic jumping. According to Tibetans, the body of those who drill themselves for years, by that method, become exceedingly light; nearly without weight. These men, they say, are able to sit on an ear of barley without bending it’s stalk or to stand on the top of a heap of grain without displacing any of it. In fact the aim is levitation.

Alexandra David-Neel, “Magic and Mystery In Tibet” p150

Sensory Association Areas

Notice how big the hands are (heavy) and how thin the arms are. This has always been the problem when reproducing Sensory Homunculus. Photo by Mpj29

One of the coolest tricks of the sensory association areas is the ability to carry information across modalities. For example, somebody handed an object of which they cannot see but can have a good feel of will be able to pick out that object when shown a choice of things. Thus a relay station exists between modalities. Synaesthesia occurs when this station relays information into unusual areas, so that someone may experience a smell as a kinesthetic shape or a sound as a colour. Most people are able to do this to a degree, for example, music is evocative of emotions and I for one attribute colours to music. For example whilst some music is colourful, i find other music to be rather black and white (dull). Greater synaesthesia is inducible with trance and is often reported by LSD and hashish users.

Vasily Kandinsky (1866-1944) was a synesthetic artist who perhaps had the deepest understanding of sensory fusion. He had stopped objective representation in his paintings after 1911, being more interested in expressing a vision than in illustrating surface reality. Kandinsky was among the first to step off the well-beaten path of representation that Western art had followed for five hundred years, and his model to express his transcendent vision was music. He explored harmonious relationships between sound and colour and used musical terms to describe his paintings, called them “compositions” and “improvisations.”

Richard E. Cytowick, The Man Who Tasted Shapes. P55.


‘When I reached the casualty, he was fully conscious but it was evident that he had suffered a serious stroke. It had affected the left side of his body, which he couldn’t move. When I asked him how he was feeling he replied cheerfully, “I’m fine, if only my brother would take his arm off me then I could get up” as he gestured to his paralysed left arm.’

Nursing casualty-report on stroke patient.

Confabulation of this kind (above) is most commonly seen in people who have suffered a stroke to the right hemisphere of the brain, particular if the affected area is the right motor cortex area. With “left hemi-neglect” these patients will literally lose the concept of leftness. When asked to draw a clock face, they will only draw half a clock, with all the numbers squashed into the right half, they will only shave the right side of their faces and will ignore any food on the left side of their plate.

Confabulation will occur as the patient explains the disparity between what the observer says the patient is doing and the actual behaviour of the patient:

What is curious is that the patient will more often than not be blissfully unaware that anything is wrong. Where we might see ‘hyper-emotionalism’ where the patient has suffered a stroke to the left hemisphere, the patient with a right hemispheric infarct will appear blissfully happy:

“The left hemisphere may claim that a paralysed left leg or arm is normal or that it belongs to someone other than the patient. This occurs in many cases because somesthetic body information no longer is being processed or transferred by the right hemisphere: the body image and the memory of the left half of the body has been deleted. In all these instances, however, although the damage may be in the right hemisphere, it is the speaking half of the brain that confabulates.”

R. Joseph, Phd.


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