Posts Tagged ‘cortex’

Hallucinations

January 8, 2019

Part of this post is taken from Helen Thomson’s book, “Unthinkable: An Extraordinary Journey the World’s Strangest Brains.”

Hearing voices that are not there is often considered a sign of mental illness. In 1973, David Rosenhan, a professor emeritus at Stanford, got himself and seven other completely healthy friends admitted to the mental wards of hospitals across the United States. The point of this experiment was to question the validity of psychiatric diagnosis, but they were surprised to find that it was so easy to be admitted as a mental patient. Each participant phoned a hospital complaining of hearing voices. The rest of their medical history and other life stories were true. All eight were admitted. Seven were diagnosed with schizophrenia, and one with manic-depressive disorder. As soon as they entered the hospital they said their hallucinations had disappeared. Then it was up to each individual to convince the staff to discharge them. This task took between seven and fifty-two days.

Most hallucinations are not associated with schizophrenia. John McGrath, a professor at the Queensland Brain Institute interviewed 31,000 people from eighteen different countries. When participants were asked whether they had ever experienced a hallucination, such as hearing voices that other people said did not exist, 5% of men and 6.6% of women responded yes.

Oliver Sacks said, “The brain doesn’t tolerate inactivity. It seems to respond to diminished sensory input by creating autonomous sensations of its own choosing.” It was noted soon after WW2 that high-flying aviators in featureless skies and truck drivers on long, empty roads were prone to hallucinations.

Psychologists believe that these unreal experiences provide a glimpse into the way our brains stitch together our perception of reality. Our brains are bombarded with thousands of sensations every second of the day. Our brains rarely stop providing us with a steady stream of consciousness. Processing everything that we experience in the world all of the time would be a very inefficient way to run a brain. Instead it takes a few shortcuts. However when this input is low or absent, it creates sensations, that is, hallucinations.

You can create your own hallucinations safely at home. All you need is a table-tennis ball, some headphones and a bit of tape. Cut the ball in half and tape each segment over your eyes, Sit in a room that is evenly lit, find some white noise to play over your headphones, sit back and relax. This is called the ganzfield technique, this technique has been used to investigate the appearance of hallucinations for decades.

Should you not want to bother with this technique you can read the following descriptions that were reported in a paper published in the journal Cortex by Jiri Wackermann at the Institute for Frontier Areas of Psychology and Mental Health.

“For quite a long time were was nothing except a green-grayish fog. It was really boring. I thought, ‘Ah, what a nonsense experiment!’ Then for an indefinite period of time, I was ‘off,’ like completely absent-minded. Then, all of a sudden, I saw a hand holding a piece of chalk and writing on a blackboard something like a mathematical formula. The vision was very clear, but it stayed only for a few seconds and disappeared again…it was like a window into that foggy stuff.’ Later, she saw a clearing in a forest and a woman who passed by on a bike, her long blond hair waving in the wind.”

Another participant felt like she and a friend were inside a cave, ‘We made a fire. There was a creek flowing under our feet, and we were on a stone. She had fallen into the creek, and she had to wait to have her things dried. Then she said to me: ‘Hey, move on, we should go now.’

Here is what the author, Helen Wilson, writes of her own experience with the ganzfield technique. “Nothing happened for at least 30 minutes, other than a myriad of random thoughts and waves of sleep. Just as I was wondering whether I should give up, I saw an image coming out from what seemed like a window full of smoke. It was of a man lying curled up next to me. It appeared for a few seconds, then disappeared. It certainly differed from a dream, or from a random image plucked from my imagination. It was an intriguing demonstration of what can occur when our senses are impaired.”

The Brain’s Secret Powerhouse That Makes Us Who We Are

July 7, 2018

The title of this post is identical to the title of an article by Caroline Williams in the Features section of the 7 July 2018 issue of the New Scientist. The cerebellum is tucked beneath the rest of the brain and only a tenth of its size. In the 19th century phrenologists, who examined the shape of the skull to determine a person’s character, declared the cerebellum to be the root of sexual desire. They thought, the larger the cerebellum, the greater the likelihood of sexual desire.

During World War 1, the British neurologist Gordon Holmes noticed that the main problems for men whose cerebellum had been damaged by gunshot wounds had nothing to do with their sex lives and everything to do with the fine control of movements, ranging from a lack of balance to difficulties with walking, speech, and eye movements. From then on, the cerebellum was considered the mastermind of our smooth and effortless motions, with no role in thinking.

In the mid 1980s when brain imaging came along researchers noted activity in the cerebellum while people were lying still in a brain scanner and thinking. Unsure as to why this was occurring it was explained away as the neural signature of eye movements.

It took until the 1990s that it became undeniable that something else was occurring. Reports emerged describing people who had clear damage to their cerebellums but no trouble with movement. They experienced a host of emotional and cognitive issues, from depression to attention problems and an inability to navigate.

By this time, advances in neuroscience made it possible to trace long-range connections to and from the cerebellum. It was found that only a small proportion of the cerebellum was wired to the motor cortex, which is the brain region involved in making deliberate movements, explaining why movement was unaffected for some people with a damaged cerebellum. The vast majority of the cerebellum connects to regions of the cortex that are involved in cognition, perception, language and emotional processing.

A review of maps of the cerebellum built from functional MRI brain scans confirmed that all major cortical regions have loops of connections running to and from the cerebellum. The cerebellum has conversations with different areas of the cortex: taking information from them, transforming it and sending it back to where it came from.

One of the more unexpected connections was with the prefrontal cortex, which lies far from the cerebellum at the front of the brain and has long been considered the most advanced part of the brain. This region is in charge of abilities such as planning, impulse control, and emotional intelligence. It is disproportionately large and complex in humans compared with our closest species.

Robert Barton, an evolutionary neuroscientist at Durham in the UK says that when compared to primate brains, he found there is something special about the ape cerebellum, particularly our own. Throughout most of mammal evolution, the cerebellum increased in size at the same rate as the rest of the brain. But when apes split off from other primates, something strange began to happen. The ape cerebellum had a runaway growth spurt, becoming disproportionately larger than it evolved in the lesser apes. In our own brains the cerebellum is 31% larger than you would expect scaling up the brain of a non-ape primate. And it is jam-packed with brain cells, containing 16 billion more than you would anticipate finding if a monkey brain were enlarged to the size of ours. By strange coincidence, there are 16 billion neurons in the entire cortex. Neurons are particularly energy hungry cells, so this represents a huge investment of resources of the kind the brain wouldn’t both with without good reason.

Barton suspects that what started this unlikely growth spurt was the challenge of moving a much larger body through the trees. While small primates can run along the branches even gibbon-sized apes are too heavy to do the same, at least without holding on to branches above. This led apes to switch to swinging through the branches, known as brachiation, which in turn made the ability to plan ahead a distinct advantage. Barton says, “Brachiation is a relatively complex locomotor strategy. It involves fine sensory motor control, but it also involved a need to plan your route so that you can avoid accidents.”

To be able to plan a route, it helps to be be able to predict what is likely to happen next. To do that, you need to make unconscious adjustments to the speed, strength and direction of your movements on the fly.

Neuroscientists believe that the cerebellum achieves this by computing the most likely outcome based on previous experience using so-called forward models. Once it has these models in place through learning, it can then update and amend them depending on what is happening now. Narebder Ramnani, a neuroscientist at Royal Holloway University in London says, “Forward models respond very quickly because they allow the brain to generate what are likely to be the correct movements without waiting around for feedback.”

The leap in motor skills that came with brachiation and forward planning doesn’t completely explain the vast increased in the size of the cerebellum. Vineyard-like rows of bushy neurons called purkinje cells are linked by parallel fibers coming from the senses and vertical climbing fibers, which are thought to carry error messenger with which to update the internal model.

This structure is copied and pasted across the entire cerebellum with processing units set up like banks of computers, spitting out predictions all day long. Unlike the cortex, the structure of the cerebellum looks exactly the same regardless of where you look or which part of the cortex it is connected to. The only distinction is that different “modules” connect to different parts of the cortex.

Ramona says, “This suggests that whatever kind of computation that the cerebellum is carrying out for the motor regions of the brain, it is likely to be doing much the same for the cognitive and emotional regions too. And if the cerebellum is learning to automate rules for movements, it is probably doing likewise for social and emotional interactions, which it can call up, adapt and use at lightning speed.

Barton believes that having the ability to learn, plan, predict and updates was a key movement in our evolution, opening up a whole new world of complex behaviors. At first, these behaviors revolved around planning sequential movements to reach a goal, such as adapting twigs as a tool for termite fishing. But eventually thinking unhooked from movement, allowing us to plan our behaviors without moving a muscle. Barton thinks that being able to understand sequences could have allowed our ancestors to decode the gestures of others, setting the stage for the development of language.

The idea that the cerebellum makes and updates forward models contribute to the understanding of how the brain builds a picture of the word around us. The brain makes sense of the cacophony of sensory information with which it is bombarded by using past experience to make predictions that it updates as it goes along. With its forward planning capabilities, the cerebellum plays a more important role in the general working of the brain than we thought.

This new thinking strongly suggests that the cerebellum is involved in everything from planning to social interactions, and has a role in a range of conditions. For example, differences in how the cerebellum and the prefrontal cortex are connected are thought to affects the ability of people with Attention Deficit Hyperactivity Disorder (ADHD) to focus.

Schizophrenia is commonly linked with cerebellum changes, which could result in an inability to balance internally generated models of reality with sensory information entering the brain.

There is some hope that giving the cerebellum a boost using a type of brain stimulation called transcranial magnetic stimulation could help. A clinical trial is under way for schizophrenia.

This stimulation could even do us all some good; a recent study found that applying it to the cerebellum of healthy volunteers improved their ability to sustain attention.

We’ve Finally Seen How the Sleeping Brain Stores Memories

December 29, 2017

The title of this post is identical to the title of a post by Jessica Hamzelou in the 7 October 2017 issue of the New Scientist. To do this research needed to find volunteers who were able to sleep in an fMRI scanner. They needed to scan 50 people to find the 13 who were able to do so. These volunteers were taught to press a set of keys in a specific sequence. It took each person between 10 to 20 minutes to master this sequence.

Once they learned this sequence they each put on a cap of EEG electrodes to monitor the electrical activity of their brains, and entered an fMRI scanner, which detects which regions of the brain are active.

There was a specific pattern of brain activity when the volunteers performed the key-pressing task. Once they stopped, this pattern kept replaying in their brains as if each person was subconsciously reviewing what they had learned.

The volunteers were then asked to go to sleep, and they were monitored for two and a half hours. At first, the pattern of brain activity continued to replay in the outer region of the brain called the cortex, which is involved in higher thought.

When the volunteers entered non-REM sleep, which is known as the stage when we have relatively mundane dreams, the pattern started to fade in the cortex, but a similar pattern of activity started in the putamen, a region deep within the brain
(eLife, doi.org/cdsz). Shabbat Vahdat, the team leader at Stanford University, said that the memory trace evolved during sleep.

The researchers think that movement-related memories are transferred to deeper brain regions for long-term storage. Christoph Nissen at University Psychiatric Services in Bern Switzerland says, “this chimes with the hypothesis that the brain;’s cortex must free up space so that it can continue to learn new information.

The title of this post is identical to the title of a post by Jessica Hamzelou in the 7 October 2017 issue of the New Scientist. To do this research needed to find volunteers who were able to sleep in an fMRI scanner. They needed to scan 50 people to find the 13 who were able to do so. These volunteers were taught to press a set of keys in a specific sequence. It took each person between 10 to 20 minutes to master this sequence.

Once they learned this sequence they each put on a cap of EEG electrodes to monitor the electrical activity of their brains, and entered an fMRI scanner, which detects which regions of the brain are active.

There was a specific pattern of brain activity when the volunteers performed the key-pressing task. Once they stopped, this pattern kept replaying in their brains as if each person was subconsciously reviewing what they had learned.

The volunteers were then asked to go to sleep, and they were monitored for two and a half hours. At first, the pattern of brain activity continued to replay in the outer region of the brain called the cortex, which is involved in higher thought.

When the volunteers entered non-REM sleep, which is known as the stage when we have relatively mundane dreams, the pattern started to fade in the cortex, but a similar pattern of activity started in the putamen, a region deep within the brain
(eLife, doi.org/cdsz). Shabbat Vahdat, the team leader at Stanford University, said that the memory trace evolved during sleep.

The researchers think that movement-related memories are transferred to deeper brain regions for long-term storage. Christoph Nissen at University Psychiatric Services in Bern Switzerland says, “this chimes with the hypothesis that the brain;’s cortex must free up space so that it can continue to learn new information.