Scientists find explanation for blindsight

June 25, 2010 by Lin Edwards, Medical Xpress report
Visually driven responses in parietal area LIP. (See the original paper for details.) Image: Nature, doi:10.1038/nature09179

( -- The rare phenomenon of blindsight has been known for a long time, but until now has never been understood. People with blindsight are effectively blind through damage to the primary visual cortex and yet may be able to identify colors and to avoid obstacles in their way even though they are not consciously aware of them.

New research on monkeys has found that loss of part of the leaves the unaware of in affected areas, but other regions of the brain appear to be involved in processing visual information, and these areas may contribute to the phenomenon of blindsight.

The researchers, Michael C. Schmid and colleagues from the U.S. National Institute of Mental Health (NIMH) in Bethesda in Maryland, worked with two with small lesions in their primary visual cortexes, which made them unaware of visual cues in a subset of their visual fields. The researchers first defined the precise areas of the visual field to which they no longer responded and then confirmed with (MRI) that stimuli in those areas could induce activity in the rest of the visual cortex.

The researchers then injected a part of the brain called the lateral geniculate nucleus (LGN) with a chemical, THIP, which activates the receptor for an inhibitory signaling molecule, and thus temporarily shuts down the LGN. The LGN is part of the thalamus in the middle of the brain and has been shown by previous studies to have projections to several secondary visual areas, which implies it may play an important role in the visual system.

The researchers tested the responses of the monkeys to high-contrast stimuli presented to the part of the visual field affected by the lesion both before and after the injection. The results showed that before the injection the monkeys exhibited blindsight responses of eye focusing movements, correct location of the stimuli, and activation of areas of the brain shown by the fMRI. After the injection there were no responses.

The findings suggest LGN may be the main relay between the retina and the main visual cortex, and projections from LGN to other parts of the brain provide a critical contribution to blindsight.

The paper is published in the journal Nature.

More information: Blindsight depends on the lateral geniculate nucleus, Michael C. Schmid et al., Nature advance online publication 23 June 2010. doi:10.1038/nature09179

Related Stories

Recommended for you

The brain learns completely differently than we've assumed since the 20th century

March 23, 2018
The brain is a complex network containing billions of neurons, where each of these neurons communicates simultaneously with thousands of other via their synapses (links). However, the neuron actually collects its many synaptic ...

How do we lose memory? A STEP at a time, researchers say

March 23, 2018
In mice, rats, monkeys, and people, aging can take its toll on cognitive function. A new study by researchers at Yale and Université de Montréal reveal there is a common denominator to the decline in all of these species—an ...

Brain's tiniest blood vessels trigger spinal motor neurons to develop

March 23, 2018
A new study has revealed that the human brain's tiniest blood vessels can activate genes known to trigger spinal motor neurons, prompting the neurons to grow during early development. The findings could provide insights into ...

Being hungry shuts off perception of chronic pain

March 22, 2018
Pain can be valuable. Without it, we might let our hand linger on a hot stove, for example. But longer-lasting pain, such as the inflammatory pain that can arise after injury, can be debilitating and costly, preventing us ...

From signal propagation to consciousness: New findings point to a potential connection

March 22, 2018
Researchers at New York University have discovered a novel mechanism through which information can be effectively transmitted across many areas in the brain—a finding that offers a potentially new way of understanding how ...

Using simplicity for complexity—new research sheds light on the perception of motion

March 22, 2018
A team of biologists has deciphered how neurons used in the perception of motion form in the brain of a fly —a finding that illustrates how complex neuronal circuits are constructed from simple developmental rules.


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (2) Jun 25, 2010
This does not explain the effect of actually blindfolded people (shamen, mystics, martial arts experts, etc) being able to find their way around with no 'visual' aids -whatsoever. I thought I'd make such a comment so that this point raised here (in this bit article), cannot be either consciously or unconsciously used to debunk a completely separate and notably different consideration.
3.5 / 5 (2) Jun 25, 2010
I don't think you need elaborate explanations involving blindsight to debunk people wandering around with blindfolds on. Old fashioned cheating is more than sufficient.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.