July, almost a distant memory now. Apologies for the slight delay in posting this month. It was due to a hearing voices conference I was organising, and not excessive Olympics watching. Honest!
The majority of this month’s papers are on the biology of the experience. Specifically were papers on:
- How ‘hearing voices’ impacts on performance on a virtual reality task.
- Mismatch negativity in people diagnosed with schizophrenia who hear voices.
- Why hearing voices may be related to the brain’s left hemisphere specifically.
- How transcranial magnetic stimulation works for voice-hearers.
- How childhood trauma is related to hearing voices.
- What areas of the brain are involved in voice-hearing (an MEG study).
Seoul, South Korea. Han and colleagues use a virtual reality program to examine how ‘hearing voices’ impacted upon people’s ability to perform tasks in a virtual reality world.
- Accessible summary: Han and colleagues devised a virtual reality program in which participants wear a headset and are immersed in a virtual house (with a bedroom, living room, kitchen and a bathroom) which they navigate using a joystick. The task was to navigate the house and find 8 specific items (e.g, toothbrush, towel, camera, etc) as quickly as possible.
- Participants did this task under 3 different conditions, 1) with ‘hallucinated voices’ played to them via headphones while they were doing the task, 2) with ‘hallucinated voices’ played to them, plus other virtual people (called ‘avatars’) in the virtual house during the task, and 3) with neither ‘hallucinated voices’ nor other people/avatars in the house. Three groups of people (people diagnosed with schizophrenia who heard voices, people diagnosed with schizophrenia who had never heard voices, and a non-patient, non-voice hearing control group) took part in the study. Performance on the task was measured in two ways, how long people took to find all 8 items, and how many times they referred to a ‘packing list’ of the 8 items they were looking for.
- It was found that ‘hallucinating patients’ and ‘non-hallucinating patients’ did not differ in the time it took them to do the task. However, it was found that ‘hallucinating patients’ checked the packing list less times than ‘nonhallucinating patients’ when unusual voices were present without avatars, but not when they were present with avatars. The authors argued that this was because the ‘hallucinating patients’ were more used to dealing with unusual voices coming from nowhere. Pardoxically though, the ‘hallucinating patients’ subjectively reported it was harder for them to ignore the artifical voices, and reported that the artifical voices interfered with them more during the task.
- Link to paper: http://content.karger.com/produktedb/produkte.asp?doi=337264
- Accessible summary. Let’s start with what the Mismatch negativity (MMN) is. Basically, when your brain hears a different sound to one it was just hearing, there is a distinct change in the electrical activity of the brain, detectable on an Electroencephalography (EEG) machine. For example, if someone was saying to you ‘goat, goat, goat, goat’ and then said ‘monkey’, we would see a distinct change in your EEG. A specific part of this change in your EEG, roughly 150–250 ms after the change occurs, is termed the MMN. It doesn’t matter whether you are aware of this change in sound or not, your brain still produces this MMN response. Fisher and colleagues found that people diagnosed with schizophrenia who heard voices, during a time when their unusual experiences were worse than normal, had a smaller MMN response on a range of tasks, compared to people without a diagnosis of schizophrenia.
- Link to paper: http://dx.doi.org/10.1016/j.schres.2012.06.004
- Accessible summary: Broadly speaking, the left hemisphere of the brain is specialised for processing the speech we hear. Basically, due to the way the brain is wired up, the left hemisphere of the brain receives auditory input directly from the right ear. For speech which is heard in the left ear, the sound is first sent to the right hemisphere, and then has to make the long trek across the brain to get over to the left hemisphere. As a result, our right ear is better at processing speech than our left ear (i.e., we have a right ear advantage)
- One way we can measure this is using the “consonant–vowel syllables dichotic
listening (DL) task”. In this, participants wear headphones and hear a range of paired consonant-vowel sounds. A different sound is played to each ear but at the same time. The person then has to say what sound they heard. In the general population, because of the right ear advantage, people are more likely to say that the sound played to their right ear, was the one they heard.
- Hugdahl and colleagues found that people with schizophrenia with more severe hallucinations (as indexed by scores on item P3 of the PANSS) got more items wrong on sounds played to the right ear. However, there was no relation between how severe someone’s hallucinations were and how many items they got wrong on sounds presented to the left ear.
- From this they conclude that these findings support a “left hemisphere speech perceptual model for AVHs”, i.e., that this study is consistent with a model in which hearing voices is a result of “spontaneous hyper-activation of the receptive language areas in the left temporal lobe”, which is what causes interference and shut-down of the perceptual system, which is why hallucinations cause interference with specifically words presented to the right ear.
- Link to paper: http://dx.doi.org/10.1016/j.schres.2012.06.019
- Accessible summary: Transcranial magnetic stimulation (TMS) involves applying a rapidly changing magnetic field to a specific part of the brain, usually the region on the border of the temporal and parietal lobes of the brain, using a gadget which looks kind of like a ping pong bat. The changing magnetic field causes an electrical field in the part of the brain beneath where the TMS is being done, and is a painless intervention. There is some evidence that this is helpful for some people’s voices, but much less knowledge about why/how this helps.
- Kindler and colleagues examined the brain changes that occurred as a result of TMS. 15 people with a diagnosis of schizophrenia who heard voices received a 10-day treatment of TMS to the left temporoparietal junction. It was found that TMS helped the voices of the participants, and that this was associated with reductions in blood flow in the primary auditory cortex, left Broca’s area and cingulate gyrus. The authors conclude that TMS which reduces the severity of voices works by reducing hyperactivity in language regions of the brain.
- Link to paper: http://dx.doi.org/10.1016/j.biopsych.2012.06.019
- Accessible summary: This study measured dissociative experiences, childhood trauma and hallucinations in 71 people diagnosed with psychosis (most of whom had a diagnosis of paranoid schizophrenia).
- Of the 71 participants, 32 reported childhood trauma (15 reported childhood sexual abuse, 17 physical abuse, 10 the unexpected death of a relative/friend, 8 a near-drowning experience, 6 assault, and 7 a transportation accident. Note, the numbers add up to more than 32 as some people had experienced multiple traumas). Both levels of childhood trauma and levels of dissociation predicted participants’ levels of hallucinations. It was also found that if participants had childhood trauma, then the higher their levels of the dissociative experience of depersonalisation were, the more likely they were to have hallucinations (i.e., depersonalization mediated the relationship between childhood trauma and hallucinations).
- The authors conclude that if hallucinations “are products of traumatic experiences, it would be of interest to first identify the existence of those experiences in the
person with hallucinations, and second, to explore whether the events that occurred during those traumatic episodes are present in the content of the voices and beliefs about them” (p. 328).
- Link to paper: http://dx.doi.org/10.1002/jts.21693
Utrecht, Netherlands. No edition of this blog would be complete without a paper from this excellent research group. In this month’s paper, van Lutterveld and colleagues used magnetoencephalography to examine what is happening in the brain when people are hearing voices.
- Not-very accessible summary (sorry): This study asked 12 people who heard voices to indicate, using a button-press, when they were hearing voices whilst inside an magnetoencephalography (MEG) machine. MEG machines detect changes in magnetic fields in the brain, allowing us to infer which areas of the brain are active when, for example, people are hearing voices. The study found that hearing voices was associated with a decrease in alpha-band power in the right inferior frontal gyrus and with a decrease in beta-band power in the left middle and superior temporal gyrus. The onset of hearing voices was also associated with a decrease in theta-band power in the right hippocampus.
- The authors interpret these findings to mean that hearing voices is “triggered by a short aberration in the theta band in the hippocampus, followed by activity in auditory areas accompanying the experience of hearing voices”. They speculate that these “aberrations” may “disturb the coherency of thoughts and perception such that there is an increased focus on internal representations collected from memory”.
- Link to paper: http://dx.doi.org/10.1371/journal.pone.0041149
That’s all for this month. Thanks to Schizophrenia Bulletin, there will be a deluge of voice-hearing papers in next month’s blog. See you then!