Of culture and tool use: tap into your left parietal cortex

Jim Barlow's SciBlog

So what's the difference between waving at a friend and hammering a nail? Beyond the obvious that one task uses a hand and the other a hammer, there is a scientific answer that speaks back to, well, the development of human culture.

Scott H. Frey

I'm referring to an interesting paper by University of Oregon neuroscientist Scott H. Frey. The paper was placed online April 28 by the Philosophical Transactions of the Royal Society B ahead of regular publication. You are reading this in a SciBlog rather than a traditional news release because Frey is traveling and not in a position to be readily available to media who may wish to cover his work.

Frey traces years of research, including his own, on task completion by healthy people and those with brain injuries. He fits the data into the historical context of human conceptualization and motor skills. His bottom line is that functional magnetic resonance imaging (fMRI) is confirming that a specific area of the brain holds a mechanism that "may reflect common origins of the human specializations for complex tool use and language."

The growing body of evidence is that a person with a brain injury has problems not only in performing but even doing a pantomime of a previously mastered skill. The data points to damage in the brain's left cerebral hemisphere. It is in this region, particularly the left parietal cortex, that the complexities of a learned skill -- the memories -- are stored. Yes, there are similar but much smaller effects in the right hemisphere.

Frey theorizes that performing gestures after a brain injury, such as the wave of a hand in greetings, is easier to than using a tool in a project because the amount of recall required is less. In essence, injury to the left hemisphere hampers one's ability to turns thoughts into action.

But is the left hemisphere, which is dominant in right-handed people, also responsible for injury-related problems in left-handed people?

Research has shown that 90 percent of people doing a motor task prefer to use the right hand. Evidence from the fossil and archaeological record suggests that right-hand bias (and left-hemisphere dominance) for manual control dates back to early humans. A paper in Science in 2001 said humans began modifying rocks for pounding at least 2.5 million years ago. Those skills contributed to the evolution of culture and language, scientists have theorized.

Frey has tested both right- and left-handed healthy adults. Using fMRI and a series of commands given to subjects, results were consistent and pointed to the left parietal region as the storage and retrieval area for motor skills. In the new paper, Frey writes that preliminary work with lefties finds largely similar results, noting that "retrieving and planning both types of actions was associated with increased activity within the same left-lateralized regions."

Frey argues that the variety of task information stored in the left hemisphere leads to "an internal praxis representation that can be used to guide contextually appropriate actions." The parietal cortex stores the sensory information as well as input about the identities of objects, and, he says, it is this combo of stored wealth that is necessary for the execution of a task.