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Tuesday, December 20, 2011

The Curious Case of the Alien Hand

The Curious Case of the Alien Hand


This article is adapted from  Mapping the Mind.

WITH AN OMELETTE when the left hand "helped out" by throwing in, first, a couple of additional, uncracked eggs, then an unpeeled onion and a salt cellar into the frying pan. There were also times when the left hand deliberately stopped the right hand carrying out a task. In one instance I asked her to put her right hand through a small hole. "I can't - the other one's holding it" she said. I looked over and saw her left hand firmly gripping the right at the wrist" -
- Patient study, Alan Parkin Explorations in Neurospychiatry Blackwell 1996 .

    Can you imagine how it would feel to be out of control of one of your hands? To watch, helplessly, as it undid your shirt buttons seconds after your other hand had done them up, or pluck goods you don't want from supermarket shelves and place them in your pocket? Worse - think of reaching out with one hand to give your lover a gentle caress, only to see the other hand come up and deliver a right hook instead. All of these things have happened to sane and otherwise quite normal-seeming people. Such events are described in the dry jargon of medical reportage, as "inter-manual conflict". Between themselves researchers call it the "alien hand" .

    Alien hands arise in people who have suffered injury to one or both of two brain areas: one is an area called the Supplementary Motor Cortex, an area of cortex on top and to the front of the cortex. The other is the corpus callosum.. Some people with alien hands, like the woman with the culinary problems, above - have had a haemorrhage or stroke. Most of the cases, however, involve people who have undergone split-brain surgery.

    Each hemisphere has local control over its own physical realm - mainly the longitudinal half of the body on the opposite side to itself. So if the right leg is to be extended, it is the left hemisphere which instigates the movement, and vice versa. Overall control, however, is vested in the dominant (usually left) hemisphere - it is here that the decision to extend the leg is made in the first place. The left brain exercises control by sending commands, mainly inhibitory ones, to the right hemisphere via the corpus callosum. The system makes for smooth running - there is only room for one boss in a single skull.

    Sever the connection between the hemispheres, however, and in certain circumstances the command system breaks down. In split-brain patients the inhibitory messages cannot pass from hemisphere to hemisphere but most of the time this doesn't matter because the two hemispheres are so well versed in their respective roles that things just carry on as normal. . Occasionally, though, the non-dominant hemisphere seems to decide that it should be involved in something which is already being handled quite satisfactorily by the left hemisphere, and without its usual line of communication the left brain has no way of stopping it from acting. The two sides can therefore find themselves fighting - literally - for control.

One woman whose brain had been surgically split found, for example, that it often took her hours to get dressed in the morning because her alien hand kept trying to dictate what she should wear. Time and again she would reach out with her right hand and select an item from the closet, only to see her left hand whip up and grab something else. Once her left hand had got a hold on something it would not let go, and she, of course, had no way of making it obey her conscious will. Either she had to put on the clothes she was clutching or call someone to help her prise her fingers open.. Interestingly, the clothes selected by this woman's alien hand were usually rather more colourful and flamboyant than those the woman had intended to wear.

 Another patient had a hand that insisted on pulling down his pants immediately after his other hand had pulled them up. A third found his alien hand unbuttoned his shirt as fast as his other hand could fasten it. MP, the woman whose hand chucked uncracked eggs into her omelette, had to put half a day aside to pack when she went away because her alien hand would systematically remove each item from her suitcase just after she had put it in.

    Most alien hands are merely irritating or comical. As one patient put it: "It feels like having two naughty children inside my head who are always arguing". Occasionally, though, alien hands seem to be intent on more than mischief. One man reported reaching out with his right hand to give his wife a hug, only to see his left hand fly up and punch her instead. M.P., too, sometimes found her alien hand would prevent her other hand from making affectionate gestures - her husband was often subjected to a tug of war as one hand reached out to embrace him while the other pushed him away.

    Despite this alien hands rarely do anything seriously violent and the world still awaits the first case of murder to be defended on the grounds that 'it wasn't me who did it - it was my hand'. Some people with alien hands have nevertheless become terrified that they might unwittingly do something catastrophic. One poor man, for instance, was frightened of going to sleep in case his hand strangled him in the night.

It is very tempting to think of the antics of an alien hand as the expression of an anarchic unconscious, let loose by the surgeon's knife. This notion chimes in beautifully with popular conceptions of neurosis - the idea that beneath our rational surface lies a naughty, child-like other self which is held in control only by some kind of cerebral police force.

However, florid psychological explanations may not be required to explain why alien hands seem to act in direct opposition to their sensible twins. It could be that , in a (literally) maladroit way, these wayward limbs are really just trying to be helpful.

The supplementary motor cortex (SMA) - the area which, in addition to the corpus callosum is implicated in alien hand - springs into action when the brain prepares to execute complex volitional bodily action.. It does not actually trigger the action itself - instead it acts rather as a motor executive, sending "move it" signals to the neighbouring motor cortex, which in turn sends the "get moving" message to the appropriate muscles. As with all other brain parts, the SMA is cross-wired - the left cortex controls the right side of the body and vice versa. Brain scans show that, in a normal brain, the SMA on both sides of the brain is activated even when action is consciously planned for only one side of the body. The activation on the side which is not actually going to move is pretty weak, but it may be enough to cause movement unless it is stopped. Normally this inhibition comes from the SMA on the side which is actually meant to move - it sends a message to its opposite number which reads, effectively: "Do not carry through .... leave this one to me."

This message passes though the corpus callosum, so in split-brain patients it does not get through. As a result both SMAs send "move it " messages to their respective limbs, even though the conscious brain had plans to move only one.

Why then, do alien hands always seem to work against a person's conscious will, rather than in service of it? One possibility is that the seemingly mischievous antics of alien hands are not designed that way at all - rather, their dogged determination to undo everything the other hand does is because that is all that is left to them.

Say there is some simple task to be done like opening a door.. The dominant hand duly does the deed. Then the alien - dragging along behind, as it always will - arrives on the scene. The task it came to help with has been done. But the hand "knows" it was sent to do something in the area and - without the leadership of a conscious, thinking mind - it does the closest thing there is to the open-door manoeuvre it came to do: it closes it.

If this is correct it begs the question of why split-brain patients do not find both hands - and legs for that matter - taking part in everything they do. In fact even the most active aliens are happy, most of the time, to cooperate with their neighbouring body parts. The author of the case study of M.P, the frustrated omelette-maker, noted:

"I was struck by how relatively infrequent her alien hand incidents were. I viewed with some trepidation her offer to pick me up at the station but was surprised by a smooth driving performance. Similarly during my first meal with her I half expected her aberrant hand to start flicking peas at unsuspecting patients. This never happened."

In fact MP's hand, like most aliens, usually only started its tricks when the task in hand was a one-handed on/off job like opening/closing; pull up/ pull down and so on. It did not seem to happen, either, when the action was a well-practised routine - using a knife and fork presented no problems, for example; nor did swimming. This might be because very familiar procedural actions become embedded in the subcortical areas of the brain and knowledge that is encoded in this way can pass from side to side of the brain via connections other than the corpus callosum .

Neat as this explanation is, it remains somehow rather unsatisfying. The idea of the alien hand as an emissary from some deeper level of the psyche has a compelling attraction which no amount of scientific illumination is likely to dispel entirely

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