March 24, 2012 §
Surgeon Gabriel Weston claims that we are in the middle of a fat epidemic. In this week’s Horizon documentary she seeks to explain a “mystery”, why she asks when we are all surrounded with ample food do some people pile on the pounds while others do not?
Weston’s documentary makes an appropriate companion piece to last week’s The Truth about Exercise. The focus this week is on appetite and individual differences. Weston tells us that there is a hunger hormone (Ghrelin) and a fullness hormone (PYY). Dr Carel Le Roux says that the gut talks to the brain and influences how hungry or full we feel.
Using a functional MRI scan Weston’s brain is shown to be normal, with limited activation in response to calorie-rich food. By comparison a scan of an obese person’s brain reveals considerable activation in areas of the brain associated with “reward-centres”, addiction and emotional responses to food. Psychiatrist Dr Samantha Scholtz says that gastric bypass surgery can change the way the brain responds to food. 21 stone Marylin Walsh underwent a stomach bypass operation at Dr Le Roux’s hospital; within weeks she had lost four stones. More interestingly she reports that she no longer desires sweet or fatty foods. Weston is shown before and after brain scans of an obese person who had a stomach bypass and while the before image demonstrated great activity in response to high calorie foods, the post-operation scan shows minimal activity just like Weston’s own scan.
The Truth about Fat is an interesting documentary but while I found Gabriel Weston’s narrative compelling I kept wondering if there were alternative explanations that were not offered. I felt that time given over to dissections of pigs to show us visceral fat might have been better dedicated to providing stronger evidence to support the theories advanced.
At the start of the programme Weston explains that the human brain evolved at a time when food was scarce and therefore is attuned to storing energy, however in today’s world with plentiful food available 24/7, behaviour that was once useful to human survival is maladjusted to modern life. An interesting theory, but why I wondered has the fat epidemic that Weston talks about only taken hold (outside of the US) in the last 2o years when for most of the 20th century food has been cheaper and more plentiful than any other time in our history. While I find Weston’s explanations quite persuasive I felt she need to go a little further to make her case completely convincing.
Another example is the former shot putter who tells us that despite being very motivated he found it impossible to increase his weight beyond a certain point. This is an interesting change of tack from the usual case studies of people trying to lose weight; however this was only one person and therefor it is impossible to say whether this individual is a one-off or representative of the wider population.
March 13, 2012 §
Anil Seth, who took part in a debate about the nature of consciousness at the Royal Institution last week, wrote ‘Consciousness: Eight questions science must answer‘. This is the third of the the Guardian’s series ‘Consciousness: The hard problem‘; the other two ‘Neuroscience and philosophy must work together‘ by Barry Smith and ‘Consciousness: why bother?‘ by Chris Frith were reviewed previously. Unlike the other two which are essays this article after a short introduction goes point-by-point through the eight questions.
Although the format does not allow Anil to select one or two main themes and to develop them in greater detail, it does make for a very accessible article and allows the reader to get an overview of some important issues very quickly.
The eight questions are:
- What are the critical brain regions for consciousness?
- What are the mechanisms of general anaesthesia?
- What is the self?
- What determines experiences of volition and ‘will’?
- What is the function of consciousness? What are experiences for?
- How rich is consciousness?
- Are other animals conscious?
- Are vegetative patients conscious?
Some of these questions, such as ‘what is the self?’ are probably as old as philosophy itself. However, modern science is providing some fresh insights into some of these questions and promises to provide future insights into others. For example one approach to answering the question, ‘what are the critical brain regions for consciousness?’, is to try to identify the neural basis of consciousness. Essentially, this means identifying what brain activity at a neural level correlates to specific experiences of consciousness; these are referred to the Neural Correlates of Consciousness.
The questions cover a broad range of subjects within the field of consciousness; most people with an interest in consciousness should find something of interest in this article. I thought the question ‘What is the function of consciousness’ particularly interesting. The best answer appears to be that consciousness integrates information. Conversely it might be expected that a lack of consciousness could reflect a breakdown in how the brain integrates information. Anil points to increasing evidence to suggest that disintegration of how different parts of the brain work together that underlies how anaesthesia works.
Anil has backed up each of the eight points with at least one link which enables the reader to look deeper into the subject. It also allows the reader to get a better understanding of the evidence on which Anil bases his writing.
Of the three articles I found this one to be the most interesting and useful, and Anil has highlighted several strands of research in the neuroscience of consciousness highlighted here that are worth following the progress of.