MEG scanning the brain

Wired has a brief guide to one of the most recently developed and exciting brain imaging technologies – magnetoencephalography or MEG.

The first thing you’ll notice about MEG machines is that they live in carefully shielded sealed rooms. The second you’ll notice is that they look like giant hair dryers.

MEG works by picking up the magnetic field generated by the brain. You might remember from high school physics that every current produces a magnetic field, meaning neurons produce a magnetic field every time they are active.

However, because even groups of active neurons only have a small current, the associated magnetic field is very weak.

So weak, in fact, that a car passing in a nearby street, and even the earth itself, produces a much stronger magnetic field. This is why the shielded room is needed.

Even with the shielding, to pick up such a weak magnetic field MEG uses ultra sensitive Superconducting Quantum Interference Devices or SQUIDs.

Because they rely on superconductors, they need to be supercooled to work. To achieve this, they’re bathed in a pool of liquid helium held in a large container above the head – this is why MEG machines look like giant hairdryers.

An advantage of MEG over EEG is that unlike electrical fields, magnetic fields travel virtually unaltered across the skull, meaning it’s possible to more accurately measure where activity comes from.

An advantage over fMRI is that MEG can measure brain changes on a millisecond by millisecond basis, meaning it’s much quicker than the typical fMRI 1 second time frame.

Also, MEG is measuring brain activity directly, rather than inferring it from changes in blood flow as fMRI and PET do.

However, as MEG only measures activity on the surface of the brain and can’t distinguish activity from small areas, it doesn’t give the full depth or spatial resolution of fMRI.

As the Wired article notes, MEG is going to become an increasingly important player in our quest to understand psychology and neuroscience, so keep a lookout for an increasing number of important findings based on MEG scans.

Link to Wired article ‘MEG Scanners Are Mega Powerful’.

Temporal typo trauma

There’s a lovely typo in a 1976 paper from the Journal of Neurology, Neurosurgery, and Psychiatry that reports on a study about epilepsy after surgery. Check out the last sentence of the abstract:

Incidence of postoperative epilepsy after a transtentorial approach to acoustic nerve tumours.

J Neurol Neurosurg Psychiatry. 1976 Jul;39(7):663-5.

Cabral R, King TT, Scott DF.

Sixty-nine patients who had neurosurgical treatment for acoustic neuroma by one of two different techniques were studied with a view to determining the incidence of postoperative epilepsy. Fourty-five patients who had larger tumours underwent a combined translabyrinthine and transtentorial neurosurgical approach. For the others with smaller neuromas a translabyrinthine method was used. Only the combined approach was associated with postoperative epilepsy, and it occurred in 22% of the patients. Epilepsy was associated with temporal love trauma during surgery.

Link to entry on PubMed.

2007-01-05 Spike activity

Quick links from the past week in mind and brain news:

A boy who can walk on hot coals offers clues to genetics of pain.

A curious report of 50 Vietnamese schools girls fainting due to ‘mass hysteria‘.

Research on how you compare yourself with colleagues and happiness at work is investigated by the BPS Research Digest.

A new chemical could provide the first highly accurate living diagnosis of Alzheimer’s disease.

A few articles on exercises for cognitive enhancement:
* The New York Times reports on brain exercises.
* Time magazine discusses ‘Nintendo for Grandma’.
* The Washington Post considers keeping sharp with mental exercises.

It seems Freud had a few troubles repressing his innermost desires, as a hotel guest book suggests.

Neurofuture has some wonderful art generated by neural networks.

Anarchic art journal MungBeing has a special issue on ‘The Mind’.

The International Herald Tribune argues that neuroscience is now explaining what might cause ‘ghosts’.

A (presumably Falafel loving) Israeli scientist argues that chickpeas may have been responsible for the evolution of the human brain.

Freedom is slavery

We have the impression that our free will is supreme, but modern neuroscience is starting to challenge the idea that we are the masters of our fate and captains of our soul.

A recent article in The New York Times looked at some of the philosophical aspects of free will from the perspective of physics and neuroscience.

Newtonian physics suggests that interactions in the physical world are deterministic, that is, the outcome is predictable.

As physical objects, a crucial question is how can we have free will in a universe where every outcome is determined by what went before.

Some people have suggested that the ‘fuzzy’ nature of quantum physics might provide an answer to this, but there have been no convincing accounts of how this might work.

In neuroscience, free will is more to do with whether we have conscious control over our actions.

Two main threads of research have suggested that our experience of having complete conscious control over our actions may be an illusion.

The first is from experiments like those originally completed by Benjamin Libet. He asked people simply to move their hand whenever they felt like it and note the time when they first felt the urge to move.

While they performed this voluntary action, he recorded electrical activity from areas in the brain known to be involved in generating actions.

His experiments, and many subsequent replications, suggest that the brain’s movement areas are active about 200 milliseconds before we feel the urge to move.

In other words, we only become conscious of the intention to move after the brain has initiated the action.

The second source of doubts about our sense of free will is from patients who have suffered brain injury and discover that they have lost conscious control over their actions.

One of the most striking examples is anarchic hand syndrome, linked to frontal lobe damage, where patients find their hand has a ‘mind of its own’ and often have to prevent it from carrying out actions they don’t consciously intend.

An article in The Economist questions whether such findings are eroding the concept of legal responsibility.

This is particularly in light of court cases where evidence of neurological disturbance has been used in an attempt to persuade the jury that the person wasn’t responsible for their actions, and, therefore, not guilty of the crime in question.

Link to NYT article “Free Will: Now You Have It, Now You Don’t”.
Link to Economist article ‘Free to choose?’ (both via 3Q).

Cognitive biases and the start of war

Foreign Policy magazine has an article by Daniel Kahneman and Jonathan Renshon on the role of cognitive biases in the decision to go to war.

Kahneman is a nobel prize winning psychologist known for his work on decision making and Renshon is a political scientist and author of the book Why Leaders Choose War: The Psychology of Prevention (ISBN 0275990850).

Social and cognitive psychologists have identified a number of predictable errors (psychologists call them biases) in the ways that humans judge situations and evaluate risks. Biases have been documented both in the laboratory and in the real world, mostly in situations that have no connection to international politics. For example, people are prone to exaggerating their strengths: About 80 percent of us believe that our driving skills are better than average. In situations of potential conflict, the same optimistic bias makes politicians and generals receptive to advisors who offer highly favorable estimates of the outcomes of war. Such a predisposition, often shared by leaders on both sides of a conflict, is likely to produce a disaster. And this is not an isolated example.

The article is an interesting attempt to apply knowledge of cognitive biases to understanding political decision making in high stress, high stakes situations.

This is an area which is becoming increasingly important in military psychology. Both to understand how individual soldiers might make battlefield decisions, and how leaders might make strategic choices during conflict.

Link to article ‘Why Hawks Win’ (via Frontal Cortex).