Getting to grips with grasping

grasping.jpg Reach and grasp a willing colleague by the arm, now let them go, and pick up a pen or pencil instead. The first movement requires a power grip, flexing all the fingers together towards the palm, the second movement uses a precision grip involving the thumb and forefinger. Easy to do? Apparently yes, but the ease and accuracy with which we reach and grasp objects (or people!) belies the complexity of the neural processing underlying such movements. Now the journal Nature Reviews Neuroscience has published a comprehensive review on the neuroscience of grasping, by Umberto Castiello.

Castiello describes how studies on the ‘kinematics’ of grasping have shown there is a reliable ‘landmark’ during reaching movements: when the hand is between 60 to 70 per cent of the way towards its target, the gap between the thumb and fingers always reaches its largest point, the precise moment correlating highly with the size of the object to be grasped. Other object characteristics – its weight, texture, surface – also affect aspects of the grasping movement in a lawful way.

Most of our knowledge about the brain networks involved in grasping come from intrusive experiments on monkeys that are simply not possible or ethical in humans. These point to a circuit involving the primary motor cortex, the premotor cortex and the anterior intraparietal sulcus. How similar things are in the human brain is a matter of controversy and ongoing investigation using brain imaging and studies with brain-damaged patients. These suggest many of the grasping-related areas implicated in the monkey brain are activated in the human brain too, but that other regions are also involved, including the prefrontal, somatosensory and cerebellar areas.

Castiello describes one patient, A.T., with extensive damage to the parietal lobe and secondary visual areas, who had problems grasping neutral, laboratory objects but was okay at grasping familiar items such as a lipstick. This suggests that, in humans at least, brain areas involved in interpreting the meaning of an object also influence the brain’s grasping circuit.

Indeed, Castiello says more research is needed into whether and how the meaning of an object, and intentions for what to do with an object, affect grasping in monkeys in the same way research has shown these more ‘cognitive’ variables influence grasping in humans.

“It will only be through careful and thoughtful experimentation, using converging techniques from the brain and behaviour, that we might completely understand the grasping function of the human hand”, Castiello’s review concludes.

Link to abstract of the review.

Is daydreaming linked to Alzheimer’s ?

buckner_study.jpgA recent brain scanning study has been widely reported as suggesting that Alzheimer’s disease is linked to the brain functions of daydreaming. The actual study is both complex and interesting, although not as clear cut as the headlines make out.

Th research project, led by neuroscientist Randy Buckner, conducted brain scans on 10 people with Alzheimer’s disease and 8 older people without, and also used data from previous studies on young people.

The newly conducted scans looked at how amyloid plaques, damaging accumulations of proteins linked to Alzheimer’s disease, were distributed across the brain. Further scans looked for other types of structural changes in the brain, such as shrinkage.

This distribution was matched with activity from the scans of young people. In contrast to the structural scans, these functional scans looked at how active the brain was.

Normally, functional scans involve participants being asked to do a particular task. In Buckner’s study, however, the activity was from participants who were just ‘resting’ and were not asked to do any specific mental activity – something the researchers called ‘default activity’.

The researchers noted that ‘default activity’ showed a similar pattern in the brain to the distribution of amyloid plaques in Alzheimer’s disease (shown in the image on the right), and have suggested there might be a link.

There are several unanswered questions though, which the researchers themselves acknowledge.

One is simply that ‘resting’ or ‘default’ brain activity is a mystery, no one is quite sure what the brain is doing in this state. ‘Daydreaming’ is just an everyday term that is used, because we assume that’s what we do when we’re not doing much.

In reality, the brain areas highlighted by the study are involved in a range of diverse of contrasting mental activities.

A further difficulty is that the correlation between ‘default activity’ and amyloid plaque distribution was found between two sets of people. More convincing would be if these distributions were found to correlate in the same people.

With these issues in mind, the final difficulty is with interpreting the results. The researchers suggest that mental activity in younger adults could be related to the later development of Alzheimer’s, but there is no clear understanding of how this happens.

My guess is that ‘daydreaming’ is unlikely to be a significant part of this explanation, although as the scientific paper only mentions it in passing, I suspect the researchers don’t think so either.

Link to press release from Washington University.
Link to Reuters story “Daydreaming activity linked to Alzheimer’s”
Link to summary of scientific paper by Buckner and colleagues.

changing diet might allow you to see infrared

Thanks to Eric Lundquis for typing this up and putting it on the internet. It’s an experiment done by the army and cited by Rubin, M. L., and Walls, G. L. (1969). Fundamentals of visual science. Springfield, Ill.: Thomas, p. 546, which is in turn cited Sekuler, R., and Blake, R. (1994). Perception (3rd ed.). Springfield, Ill.: Thomas, pp. 62-63:

The following story dramatizes how photopigments determine what one can see. During World War II, the United States Navy wanted its sailors to be able to see infrared signal lights that would be invisible to the enemy. Normally, it is impossible to see infrared radiation because, as pointed out earlier, the wavelengths are too long for human photopigments. In order for humans to see infrared, the spectral sensitivity of some human photopigment would have to be changed. Vision scientists knew that retinal, the derivative of vitamin A, was part of every photopigment molecule and that various forms of vitamin A existed. If the retina could be encouraged to use some alternative form of vitamin A in its manufacture of photopigments, the spectral sensitivity of those photopigments would be abnormal, perhaps extending into infrared radiation. Human volunteers were fed diets rich in an alternative form of vitamin A but deficient in the usual form. Over several months, the volunteers’ vision changed, giving them greater sensitivity to light of longer wavelengths. Though the experiment seemed to be working, it was aborted. The development of the “snooperscope,” an electronic device for seeing infrared radiation, made continuation of the experiment unnecessary (Rubin and Walls, 1969). Still, the experiment demonstrates that photopigments select what one can see; changing those photopigments would change one’s vision.

Cultural cognition update

As an update to the last post, on cognitive differences between Eastern and Western societies, Richard Nisbett was on BBC All in the Mind last night to discuss his findings.

He talks about the experimental results just released, as well his wider studies which have resulted in his book The Geography of Thought: How Asians and Westerners Think Differently – And Why.

Link to All in the Mind webpage for Tuesday’s edition.
Realaudio of programme.

Chinese and Americans differ in visual analysis

asian_girl.jpgAn experiment conducted by psychologist Richard Nisbett suggests that Chinese and American people analyse scenes differently. The Americans focused on the main object in the picture, while the Chinese took a more holistic approach, and examined more of the visual context.

Traditionally, Western societies are characterised as ‘individualistic’ and Eastern societies as ‘collectivist’, suggesting that in countries like China and Japan, the focus is on society as a whole, rather than each person’s individual characteristics.

Some have suggested that this reflects the different philosophical traditions of these cultures, with the West tending to approach problems by analytically breaking them down into component parts, and the East looking at problems in their wider context.

Nisbett’s experiment suggests that this tendency may influence mental function even on the unconscious level, as his effect was found when participants were simply asked to view pictures, while their eye movements were tracked with an infra-red camera.

Importantly, the participants were unaware of the full intention of the experiment, and were told they were taking part in a study to test memory for pictures.

Why the picture of the Chinese girl? I just thought she looked beautiful.

Link to write-up from Science (with good example of eye-tracking result).
Link to New Scientist story.
Link to Scientific American story.

Cabinet on neural network pioneer Walter Pitts

walter_pitts.jpgAn article from art and culture magazine Cabinet discusses the prodigious and tragic life of neural network pioneer Walter Pitts, who was one of the major forces in the early development of computational models of the mind and brain.

Pitts started attending university lectures, uninvited, during his teenage years, and by the age of 17 was working with neurophysiologist Warren McCulloch. As Pitts was homeless and without an income at the time, McCulloch invited Pitts to live in the family home.

Together, they wrote one of the foundational papers in cognitive science, where they demonstrated that individual neurons, mathematically modelled, could be combined in networks to simulate logical computation. This suggested that such neurons could be the basic units of an information processing model of the mind.

This was a big step forward, as it suggested a potential link between the mind and brain to a science that was trying to break free from previous behaviourist ‘stimulus-response’ theories, by adopting a computational framework.

This broad approach is now the dominant theory in modern psychology, although Pitts’ was convinced of a more strictly logical model than is generally accepted today.

Pitts was completely absorbed in his work and often seemed troubled when not focused on it. It was rumoured he may have suffered from schizophrenia on account of his markedly odd behaviour and difficulties with social interaction.

Pitts moved to work with a research group in Boston, but fell out with another group member who had a disagreement with Pitts’ mentor Warren McCulloch. Pitts became a recluse and it has been rumoured he committed suicide.

Many artificial neural networks are based on his work, which are used as theoretical models of the mind, and to solve practical problems in technology and industry.

Link to Cabinet article on Walter Pitts.
Link to Wikipedia article on Walter Pitts.

BBC Click Online on ‘Blue Brain’ simulation project

neurons_getty_203.jpgBBC Technology TV show Click Online recently visited the team behind the (somewhat unlikely) claim that they are intending to ‘simulate the whole brain‘ with a supercomputer.

Despite the hype surrounding the launch, the project should be genuinely useful in producing simulations that will allow the function of individual brain cells and theories about more complex neural networks to be modelled and tested.

BBC Click Online went to the project’s base in Lausanne in Switzerland, and discussed the potential for advancing the field of neuroscience with the team. Video is available as a realvideo stream from the link below.

Link to programme information and realvideo streams.
Link to Blue Brain project.