By : Bettina Thraenhardt
How do these perceptions come about in the absence of external stimuli? As Bock explains, acoustic hallucinations may arise from “too much inside” or “too little outside.” On one side of this theoretical coin, Bock suggests that, psychologically, some affected people may hold too much on the inside. Sufferers have often experienced some kind of trauma as a child or adult, such as neglect, abuse, rape or a severe accident. Many then suffer from unresolved confl icts or find themselves in situations that overwhelm them. In these cases, verbal hallucinations may serve as signals that they need to pay attention to their own inner voice.
From a neurobiological perspective, the notion of “too much inside” makes sense in that some sufferers appear to interpret their own thoughts as alien. Some researchers therefore suspect that the hallucinations involve a failure in a specifi c feedback circuit in the brain, which normally tells us that “I” am now thinking or speaking, not someone else. This hypothesis— that self-generated speech gets misattributed— seems to apply especially well to hallucinating schizophrenics, about whom researchers have the most information.
Philip K. McGuire and his colleague Louise C. Johns of the Institute of Psychiatry at King’s College London tested the model by having several schizophrenic patients, as well as people with no psychiatric history, speak into a microphone. At the same time, the test subjects listened to their voices, distorted by the researchers, through headphones. The participants were asked to press a button if they thought they were listening to themselves. In general, the schizophrenics had greater diffi culties identifying their own voices. Those who had active hallucinations most often attributed their speech to an external source, particularly when what they said into the microphone was disparaging or contemptuous.
Studies using brain-imaging techniques have also elucidated the physiological mechanisms that underlie verbal hallucinations. In 1993 McGuire and his colleagues scanned the brains of 12 schizophrenics while they were hearing voices and while they were not. They found that during the hallucinations the greatest increase in brain activity took place in Broca’s area, a region involved not in hearing speech but in producing it. Other speech- processing areas of the brain, including the superior temporal gyrus in the left temporal lobe, are under close scrutiny. This gyrus, or bump, is responsible for speech perception and plays a crucial role in the integration of acoustic and speech information. Various researchers, among them Thomas Dierks of the University of Bern in Switzerland, have demonstrated that it also plays a key role in verbal hallucinations.
In 1999 Dierks, who was then at the University of Frankfurt, and his co-workers used functional magnetic resonance imaging (fMRI) to observe the brains of three schizophrenic patients while they were hearing voices. In addition to the superior temporal gyrus, they found activity in the primary auditory cortex, which normally processes sounds from the outside world. No wonder these patients believed their hallucinations were real: their brains responded to them much as they did to actual speech. Several other studies have produced intriguing fi ndings, among them that the left superior temporal gyrus seems consistently smaller in patients with severe acoustic hallucinations. Exactly what this size difference signifi es is still the subject of speculation.
On the fl ip side of Bock’s theoretical coin, hearing voices is not always a consequence of neurobiological change. Sometimes the brain simply receives too few stimuli from the outside world. People who hear voices often live extremely withdrawn lives—and the hallucinations, in turn, fuel social rejection. Some sailors and hikers, for example, who have endured stimulus-poor conditions for prolonged periods have reported auditory hallucinations. Indeed, Rilke’s angel spoke only after he had lived for two months in isolation at Duino Castle. Deafness, too, can present a kind of isolation. In 1992 Detlef Koempf, a neurologist at the University Medical Center of Schleswig-Holstein, Germany, discovered that musical hallucinations are not uncommon in older peoplewho have lost some hearing. He hypothesizes that the brain stores auditory information that it has captured over an extended period. If the external output is cut off, the deposited signals may take on a life of their own.
Whether hearing voices presents a medical problem depends largely on how much a person suffers. A Dutch team headed by Marius Romme, then at the University of Maastricht in the Netherlands, found signifi can't differences in the types of auditory hallucinations experienced by schizophrenics and people who were psychiatrically normal.Both groups reported dialogues, running commentary or the vocalization of their own thoughts. The mentally ill, however, far more frequently described negative voices: “You stupid idiot!” or “As usual, you revealed our family secrets!” The other study participants usually heard benign voices that encouraged them: “Come on, you can do it!” or “It really wasn’t your fault.” In addition, they were more likely to feel that they were in control of the voices.
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