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The following was taken from a long article in New Scientist 26/2/00 MIEKO had no quality of life any more, says her surgeon Ali Rezai from theCleveland Clinic in Ohio. For 15 years, she'd coped with Parkinson's disease, but then her medication began to fail her, and she found herselfalternating between the uncontrollable wild movements created by her drugs and being locked motionless. For Antonia it was a different story. She had endured agonising pain around her face for seven years since an operation to relieve the pressure of a blood vessel against a nerve. Drugs did nothing. Last month, both found instant relief when Rezai implanted a small electronic pace-maker-like device deep inside their brains. Such devices appear to work by interrupting the excessive neuronal firing that causes chronic pain or by smoothing out the strange rhythmical brain activity that causes rigidity and tremors, much as a heart pacemaker flattens the unusual beat rhythms of a fibrillating heart. They aren't a new way of dealing with pain or Parkinson's disease stimulating the spine tointerrupt pain signals was first used in the 1960s. But, if a controversial new theory is correct, surgeons like Rezai may soon be getting ready to fitthese "pacemakers" in a whole new group of patients with psychiatric conditions such as obsessive compulsive disorder (OCD) and depression, or desperately distracting sensations such as ringing in the ears (tinnitus) or schizophrenic hallucinations. According to Rodolfo Llinas, a neuro-scientist at the New York MedicalCenter, and Daniel Jeanmonod, a neurosurgeon at the University Hospital inZurich, these conditions are united by a common feature. The researchers believe that they are all characterised by strange, slow rhythms of neuralactivity originating in a walnut-sized brain region called the thalamus. This activity, they say, looks just as though one tiny part of the brain has fallen asleep. The resulting disruption in the flow of signals to the rest of the brain would produce the abnormal patterns of activity that could account for bizarre perceptions and neurological symptoms as wide-ranging as tinnitus and depression. Until recently, the thalamus was considered to be no more than a simple relay station sitting at the top of the brainstem, controlling the flow of information from our senses to the brain's outer cortex. But interest in the region has grown since neuroscientists discovered that when we're awake, it is working overtime, passing on and modifying fast "gamma" rhythms of activity to the cortex that seem to equate to conscious perception (New Scientist, 30 October 1999, p 28). It's by no means a one-way flow of information. Within milliseconds of receiving information from the thalamus, the cortex returns a signal indicating which information might be worth dealing with. The thalamus filters out what appears irrelevant and reinforces the relevant by sending more signals back to the cortex. "You can't think thalamus without cortex, or vice versa," says Jeanmonod, "It's a recurrent interplay between the two." But it is not only the physical connections between the thalamus and cortex that guide the passage of sensory infomation. The different activity patterns of sleep or waking states are also important. Llinas describes the thalamusas a "central switch" for sending the brain to sleep. When we fall asleep,the thalamus lets very little information through. It becomes less excitable,lowering its level of activity to a slow, rhythmical pattern the"theta"and "delta" rhythms and effectively dis- connects us from theoutside world. Llinas was one of the first to detect the switch from waking to sleeping rhythms in individual thalamocortical neurons, back in 1982. He discovered that the switch could be triggered by altering the chemi- calenvironment orthe electrical charge of the outer membrane of the cell. More recently, he wondered what effect switch- ing from fast to slow rhythms would have if it occurred at the wrong time: "It would be like having one part ofyour brainasleep," he says. But what would this then do to the cortex? Howmight thisalter peo- ple's perceptions of the outside world, and theirhealth? "Itwould be terrible if you got stuck in any one of thesesituations." One of the first groups of patients Llinas looked at with these ideas inmindwere people with Parkinson's disease, who were experiencing limb tremors. He noticed that their muscles were twitching in time to a theta rhythm between three and six twitches every second. At the same time, he was able to record electrical activity across the brain using a technique called magnetoencephalography, or MEG, and found the same rhythmic activity appearing in the areas of the cortex that were responsible for initiating and sensing movement. He suspected that the rhythms originatedin theregion of the thalamus connected to these cortical areas (Neurology^vol 46,p 1359). This set him wondering whether some- thing similar could occur in partsofthe thalamus related to other areas of the ner- vous system, such asthevisual, auditory and emotional areas, and not just in thoseregionsresponsible for movement. Meanwhile, Jeanmonod had been recording electrical activity directly inthebrains of patients with Parkinson's disease and chronic pain who hadbeenreferred to him for brain surgery because they had failed to respondtonormal drug treatment. Like many surgeons, Jeanmonod routinely destroyed small parts of thethal-amus in order to bring Parkinson's tremors under contro a common alternative to implanting a pacemaker. This approach was decades old,even though surgeons had only the vaguest idea of how it could relieve symptoms.The problem, however, was that some patients suffered severe side effects,ranging from defects in language and analytical thinking to paralysis, when surrounding brain tissue was damaged. Jeanmonod hoped that by recording the activity in the thalamus, using tiny electrodes implanted during exploratory surgery, he would be able to pinpoint exactly which areas were abnormal, and so target his surgery more precisely. He found the sleep-like theta rhythms in the thalamus in patients with Parkin- son's disease and chronic pain when they were awake. Just as Llinas had suspected, Jeanmonod managed to pin the rhythms down to two neighbouring regions of the thalamus, which together are responsible forpassing on movement and pain sensa- tions. By destroying only the affected part of thethalamus, Jeanmonod was able to considerably improve the outcome of his surgery, and has now operated on more than 50 people with Parkinson's,and more than 100 with chronic pain, using theta rhythms for guidance ------------------------------------------------- Nigel Cockle 59 Norley Road, Cuddington, Northwich, Cheshire. CW8 2JY England Tel +44 1606 882150 Email [log in to unmask] -------------------------------------------------