What’s a few billion neurons between friends?

March 14, 2012 § Leave a comment

Reading through various articles linked by Anil Seth’s piece in the Guardian that I reviewed yesterday one in particular caught my attention. The article, ‘How many neurons make a human brain? Billions fewer than we thought‘, reports on the research of Dr Suzana Herculano-Houzel that indicates that the healthy human brain contains about 86 billion neurons; this is 14 billion less than widely quoted figure of 100 billion.

Dr Herculano-Houzel’s methodology has attracted attention.  She took the brains of four adult males and reduced them to a “brain soup” then counted the number of cell nuclei belonging to neurons from a sample of the “soup”. From this she was able to estimate that the total number of neurons in the brain. The advantage of this method over taking a count of neurons from a sample of a specific brain region is that it is not affected by the differing density of neurons found in different areas of the brain.

However, it was not the methodology that I was most interested in. What surprised me is that the previous estimate of 100 billion neurons has been widely quoted despite no one seeming to know where the figure came from. It seems strange that science, a field of inquiry that should be rigorous and reliable, should accept a figure that cannot be verified. Which reminds me of a figure often repeated in relation to dieting and weight loss – but that’s for another day.

That aside how important is this research? 14 billion neurons are we are told roughly that of a baboon brain or half that of a gorilla brain. This gives some idea of the large number of neurons that the human brain contains in comparison to other primates. The human brain is typical for a primate except for the number of neurons; it would seem that for brains at least it is size that matters.


Consciousness: Eight questions science must answer (Review)

March 13, 2012 § Leave a comment

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:

  1. What are the critical brain regions for consciousness?
  2. What are the mechanisms of general anaesthesia?
  3. What is the self?
  4. What determines experiences of volition and ‘will’?
  5. What is the function of consciousness? What are experiences for?
  6. How rich is consciousness?
  7. Are other animals conscious?
  8. 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.

Consciousness: why bother? (Review)

March 8, 2012 § Leave a comment

The second article in the Guardian’s series about consciousness comes from Professor Chris Frith, professor emeritus at the Wellcome Trust Centre for Neuroimaging at University College London.

Professor Frith cites some useful examples of phenomenon that clarify the relationship between mind and brain. For example, he tells us about how damage to visual areas of the brain resulting in “visual agnosia” can lead to the paradoxical situation of people who are unable to recognise an object from its shape but can nonetheless adjust their hands to grasp the object when picking it up.

Much of the article, while interesting, did not offer a great deal of insight into recent developments in our understanding of the brain. Indeed, many of the examples were strongly reminiscent of Oliver Sacks’ book ‘The Man Who Mistook His Wife for a Hat‘ that was first published in 1985.

Perhaps I was expecting too much from a professor in a neuroimaging centre, however I would have liked Professor Firth to have focused more on experiments such as those into “change blindness”. These are experiments in which the subject is unable to detect a change in stimuli, for example two similar pictures that are rapidly presented to the subject. Yet the brain scanner is able to detect distinct brain activity that indicates the change has been detected even if the subject is not aware of it.

Also interesting was Professor Firth’s own area of research into the value of sharing conscious experiences. Professor Firth’s research group found that as a result of this sharing it was possible on the experimental task for two individuals to reach more accurate results than either individual on their own.

Although not the article I was hoping for it is nonetheless very interesting and informative. It also ends with a helpful list of links for further reading.

Neuroscience and philosophy must work together (Review)

March 6, 2012 § Leave a comment

Tomorrow the Royal Institution holds a debate on the nature of consciousness entitled ‘Consciousness: The hard problem‘.  Dr Anil Seth, Professor Chris Frith and Professor Barry Smith will take part in the debate. They have also contributed thought provoking articles for the Guardian in the run up to the event.

The latest of these articles comes from Professor Barry Smith, director of the Institute of Philosophy at the School of Advanced Study, University of London. The article ‘Neuroscience and philosophy must work together‘ is a readable overview of what could be a dry and difficult area. However, I found that while he does indicate how philosophy can benefit from new evidence arising from neuroscience, the article failed to explain why he believes neuroscience and philosophy must work together. Any philosophy of consciousness must take account of  new information about what is going on in the brain which neuroscience is providing.

“Now we are also learning more and more from neuroscience and neurobiology about how much of what we do is the result of unconscious processes and mechanisms.”

Professor Smith doesn’t explain what neuroscience has to gain from philosophy or how the two working together would be beneficial. Perhaps part of the answer is that philosophy has something to offer where science comes up short.

“… it must be the brain that gives rise to consciousness and decision-making. So how does consciousness arise in the brain? Science still has no answer.”

Maybe, but this would be to relegate philosophy to the role of to a sort of stand-in science, there as a place-holder until the real science is ready to step in.

This I would object to not least because there is one branch of moral philosophy that I believe should always have a role in any field of science – ethics. As we learn more about what make us who we are, and about the neuroscience that underpins our identity, the more important it is that a firm grasp of the ethical issues involved in investigating and using this information becomes.

More fundamentally I believe it is a mistake to view philosophy and science as two completely separate (and as seems apparent from some responses to the article – incompatible) phenomenon. Both philosophy and science are ways of knowing, in this case knowing about consciousness. Neurobiology can investigate consciousness at a biological level, whereas philosophy seeks to understand knowledge and the nature of knowledge.

Philosophy therefore has a role to play in two ways. First, philosophy of science is necessary to make sense of scientific findings. While the philosophy of science may not be made explicit it is always there, for example when scientists use inductive reasoning formulate theories  or derive conclusions  from their experiments using deductive reasoning.

Second, because philosophy operates at a higher level than the hard sciences it is able to provide a context in which findings from different fields of science can be understood. Not that I am suggesting that every multi-disciplinary team requires a philosopher to act as interpreter between scientist operating in different specialisms but rather that they are probably applying philosophy on some level even if they are not, dare I say, conscious of it. For example, doctors with observations about the behaviour of patients with different brain injuries talking with scientists who carry out brain-imaging on subjects undergoing different activities, can each benefit from the knowledge of the other. This benefit will be operating at a level of abstraction higher than discussions of lesions to specific brain regions or the actions of specific neurotransmitters.

Moreover, it is unnecessary to operate some sort of league table for the usefulness of different fields of inquiry. Philosophy has a role in investigating and explaining consciousness I am sure, however, I feel Professor Smith’s article is a missed opportunity for making this role clear. Hopefully, once the debate has taken place follow-up articles will explain more clearly how and why neuroscience and philosophy must work together.

in two minds about the divided brain

November 16, 2010 § Leave a comment

When I was a psychology student we learned all about the lateralization of brain function. For example, reasoning appears to be dominated by the left brain, while the right brain dominates in matters artistic. Some advances in understanding lateralization has been made due to observations by neurologists and others of functional deficiencies of people with damage to regions their brains. Oliver Sacks details some interesting cases in his book ‘the man who mistook his wife for a hat‘.

However, the view of the brain as a collection of highly specialised components, is too simplistic. Such a view fails to explain the phenomenon of neuroplasticity. Indeed, substantial damage to one hemisphere does not necessarily mean that the sufferer will lose all artistic skill or all language skill (dependent on which hemisphere is damaged) as the surviving hemisphere often takes over the functions believed to be normally governed by the damaged hemisphere.

The debate on lateralization of the brain has been given a shot in the arm by Iain McGilchrist who considers that the significance of the two hemispheres “… was that the difference lay not in what they do, but how they do it”. For example,

“… the right hemisphere was capable of appreciating ambiguity, the implicit and the metaphorical, where the left hemisphere tended to require certainty, the explicit and the literal; the right hemisphere saw the broad context and the world as a seamless whole, interconnected within itself…”

Iain's book "The Master and his Emissary"The Master and his Emissary

If you want to know more about Iain’s theory a good place to start would be hisinterview with frontier psychiatrist. The introduction to his book The Master and his Emissary is available for download from his websitehttp://iainmcgilchrist.com/

Iain also explains his theory on a podcast of Andrew Marr’s Start the Weekprogramme for Radio 4, Mon, 15 Nov 10 (N.B. the programme is 42 minutes and Iain’s main contribution comes towards the end).

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