Non-Visual Processing in the Visual Cortex

By Neuroskeptic | August 26, 2015 4:54 pm

Are there areas of the cerebral cortex purely devoted to vision? Or can the “visual” cortex, under some conditions, respond to sounds? Two papers published recently address this question.

First off, Micah Murray and colleagues of Switzerland discuss The multisensory function of primary visual cortex in humans in a review paper published in Neuropsychologia.

They criticize the conventional view that the primary visual cortex (in the occipital lobe) is little more than a reception point for signals coming from the eyes, via the optic nerve and thalamus. Instead, Murray et al. say, these parts of the brain also receive input from other sensory modalities – e.g. from the auditory cortex:

The primary visual cortex is inherently multisensory… there is a growing number of studies reporting the presence of connectivity between the primary visual cortex and primary auditory cortex (as well as other higher-level visual and auditory cortices)…

Several independent laboratories have now demonstrated that non-visual stimuli enhance the excitability of low-level visual cortices within the occipital pole.

While Murray et al. focus on studies of healthy adult brains, another team of researchers recently showed non-visual processing in the visual cortex of congenitally blind individuals. Marina Bedny and colleagues of MIT published their results in the Journal of Neuroscience: “Visual” Cortex Responds to Spoken Language in Blind Children.

Using fMRI, Bedny et al. show that sounds, especially spoken language, elicit activation in (what would normally be) the visual cortex of children born blind. This was not true of sighted children, even if they were wearing blindfolds. This suggests that the brains of the blind children had adapted, through some kind of neuroplasticity, to re-purpose the “visual” cortex to process sounds.

Bedny_blind

This result is striking, but it makes sense if we follow Murray et al. in believing that the “visual” cortex is inherently multisensory. If the normal brain contains auditory inputs to the visual cortex, maybe what happens in blind people is a strengthening of those existing connections?

Then again, it’s one thing to show that auditory signals can be transmitted into the visual cortex. But what is the visual cortex doing with this information – if anything?

I wonder what would happen if someone were to suffer a brain lesion that disconnected their visual cortex from non-visual inputs. Would they show any noticeable symptoms?

In blind people, there is evidence that the occipital cortex plays a functional role in Braille reading, a tactile (touch) modality. But common sense would suggest that these areas are functionally vision-specific in sighted people. Except for those of us with synesthesia, it seems like there’s a qualitative difference between hearing and seeing. Maybe this intuition will turn out to be wrong.

ResearchBlogging.orgBedny M, Richardson H, & Saxe R (2015). “Visual” Cortex Responds to Spoken Language in Blind Children. The Journal of Neuroscience, 35 (33), 11674-81 PMID: 26290244

Murray MM, Thelen A, Thut G, Romei V, Martuzzi R, & Matusz PJ (2015). The multisensory function of primary visual cortex in humans. Neuropsychologia PMID: 26275965

CATEGORIZED UNDER: fMRI, papers, select, Top Posts
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  • Estelle N.

    Thank you for this article, these are interesting questions on the topic. Wouldn’t it be in favour of an holistic view of brain functioning ?
    Also, how could our intuition that there is a qualitative difference between seeing and hearing turn out to be wrong as long as we experience it to be real ?

    • ddsouza

      Our intuitions often turn out to be wrong. For instance, when someone is speaking to us, we think we hear discrete words and pauses between each word – but in actual fact we are usually hearing one long continuous sound (sometimes with pauses inside a word). But our brain has learnt to interpret this long continuous sound as discrete words and pauses between each word. Our intuitions often tell us something different from reality.

      • ddsouza

        Not that I’m saying that there’s no difference between visual and auditory stimuli. But the question is whether these are processed separately or not. Our experiences are context-dependent and almost always multi-sensory, and we very rarely need to focus on only one aspect of our environment (except when we are participants in psychology experiments!).

  • Joe Bathelt

    There is a theoretical model that tried to incorporate both the specificity of cortical areas for processing specific input from a modality with their apparent capacity to process information from other modalities. According to the meta-modal organisation hypothesis, patches of the cortex compete for processing a type of information. The areas that are best suited for the processing due to cell types, prior experiences, anatomical connections etc., win and are usually processing this type of information. However, when these areas are not pre-occupied with processing their preferred input, their processing resources can be un-masked. There are experiments with typically sighted volunteers, who showed processing of non-visual information in the occipital cortex after a few days of wearing a blindfold.

    On the other hand, there is likely to be re-organisation of cortical hierarchies in congenitally blind individuals as suggested by histology and neuroimaging. It appears that typically visual areas act more likely higher-order association areas in congenitally blind adults. Consistent with this idea, activation of visual areas has been found in a range of tasks in congenitally blind individuals, including Braille reading, touch discrimination, verbal working memory, and semantic judgements.

    There is a great review on this topic by Uta Noppeney:
    Noppeney, U. (2007): The effects of visual deprivation on functional and structural organization of the human brain, 31(8), 1169–1180. doi:10.1016/j.neubiorev.2007.04.012

    • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

      That’s really interesting, thanks!

      • ddsouza

        Some people might find Michael Anderson’s (2014) book interesting: After Phrenology: Neural Reuse and the Interactive Brain

  • CL

    Close your eyes, do not think of a pink elephant….

    As mental imagery will activate the visual cortex, I think it will be very difficult to conduct an experiment where auditory stimuli does not evoke some sort of visual association. So what I am saying is that the visual cortex may still be vision specific, only that any percept we have will be made “holistic” through the process of turning an input signal into an “experience”.

    • Anonymouse

      I agree, except that nothing is “made” holistic. The brain learns to discriminate experiences using whatever input it gets, which will automatically lead to seeing something, even without actual visual input, to the degree that visual input hasn’t been discriminated from everything else (which would be highly inefficient in a world where, say, sound and sight aren’t actually independent of one another – it’s funny that google called something similar, though modularity specific, a problem in their neural network when they talk about the dumbbells: http://googleresearch.blogspot.de/2015/06/inceptionism-going-deeper-into-neural.html). So the visual cortex will basically always be active to some degree.

      The problem, then, is assuming that there’s this separate thing that is vision and a corresponding area in the brain in the first place. Neither is the visual cortex only active when visual input is given, nor does visual input only activate the visual cortex. What is gained from a view that modularizes something discretely that with experience can’t be modularized? What does it mean that the visual cortex “may still be vision specific” then? With growing experience the brain ought to become more differentiated in ways that are biased by anatomy and the experiences we share to a huge degree. So yes, the visual cortex does mainly vision. But it’s not the case that the visual cortex *is* vision. It’s also involved in all kinds of other stuff, just to a lesser (and lesser) degree. But when that experience systematically changes (like in blind people), then how could their brains not change accordingly?

      I mean, this is sort of the whole point why the embodiment movement is a joke, at least in the way it’s set up (even though some of the things that are actually being done are absolutely worthwhile http://journal.frontiersin.org/article/10.3389/fpsyg.2013.00058/abstract). Because if you understand learning, then embodiment is the same thing as liquids tasting like strawberry when they’re red. And it doesn’t work by associating discrete, independent systems and making them holistic, but it’s the default because the experience necessary to tell red liquids and strawberry taste fully apart is lacking.

      It also provides a way to think about testing this. Because the visual cortex should become more vision-specific over the course of a person’s life. I’d love to see that kind of work, although vision isn’t exactly my field.

    • Maia

      Important point! Hope some of the right people are listening…

  • Joanne Williams

    This is really interesting. I’ve heard people criticize the emerging rodent vision field with “rodent V1 is nothing like primate V1 because rodent V1 neurons also respond to sounds”.

    • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

      Ah, well maybe this research provides a rebuttal to those criticisms.

  • Nacho Sanguinetti

    This is now becoming more evident. And its not just that the signals are being transmitted there, but are processed. Cells in primary cortices of rodents respond crossmodally and code for the stimulus. Just as an example it was show that V1 codes crossmodally for somatosensation. Rodent primary cortices seem much more multisensory than what was previously thought.

    http://www.pnas.org/content/108/37/15408.long

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Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.

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