You Can Count On It: Both Hemispheres of the Brain Process Numbers

Neuroscientists of the Jena University show the visual number form area in the brain.

The human brain works with division of labour. Although our thinking organ excels in displaying amazing flexibility and plasticity, typically different areas of the brain take over different tasks. While words and language are mainly being processed in the left hemisphere, the right hemisphere is responsible for numerical reasoning. According to previous findings, this division of labour originates from the fact that the first steps in the processing of letters and numbers are also located individually in the different hemispheres. But this is not the case, at least not when it comes to the visual processing of numbers.

Neuroscientists of the Friedrich Schiller University Jena and of the Jena University Hospital discovered that the visual processing of numbers takes place in a so-called ‘visual number form area’ (NFA) – in fact in both hemispheres alike. The Jena scientists were the first to publish high resolution magnetic resonance recordings showing the activity in this region of the brain of healthy test persons. The area is normally difficult to get access to.

In their study Dr. Mareike Grotheer and Dr. Gyula Kovács from the Institute for Psychology of Jena University as well as Dr. Karl-Heinz Herrmann from the Department of Radiology (IDIR) of the Jena University Hospital presented subjects with numbers, letters and pictures of everyday objects. Meanwhile the participants’ brain activity was recorded using magnetic resonance imaging (MRI). The researchers were able to clearly identify the region in which the visual processing of numbers takes place. The small area at the underside of the left and right temporal lobe reacted with increased activity at the presentation of numbers. Letters and other images but also false numbers lead to a significantly lower brain activity in this area.

Although the Jena team already knew from other scientists’ previous research where they had to look for the area, a lot of developmental work went into the newly published story. “This region has been a kind of blind spot in the human brain until now,” Mareike Grotheer says. And here is why: Hidden underneath the ear and the acoustic meatus, surrounded by bone and air, previous MRI scans showed a number of artefacts and thus obstructed detailed research.

Image shows brain scans on a computer screen.
Researchers of the Jena University and the Jena University Hospital discovered that the visual processing of numbers takes place in both hemispheres of the brain. Credit: Jan-Peter Kasper/FSU.

For their study the Jena scientists used a high-performance 3 tesla MRI scanner of the Institute of Diagnostic and Interventional Radiology (IDIR) of the Jena University Hospital. They recorded three-dimensional images of the brain of the test subjects at an unusually high spatial resolution and hence with only very few artefacts. In addition these recordings were spatially smoothed whereby the remaining ‘white noise’ could be removed. This approach will help other scientists to investigate a part of the brain that until now had been nearly inaccessible. “In this region not only numbers are being processed but also faces and objects,” Prof. Kovács states.

About this neuroscience research

Source: Ute Schoenfelder – Jena University
Image Source: The image is credited to Jan-Peter Kasper/FSU
Original Research: Abstract for “Neuroimaging Evidence of a Bilateral Representation for Visually Presented Numbers” by Mareike Grotheer, Karl-Heinz Herrmann, and Gyula Kovács in Journal of Neuroscience. Published online January 6 2016 doi:10.1523/JNEUROSCI.2129-15.2016


Neuroimaging Evidence of a Bilateral Representation for Visually Presented Numbers

The clustered architecture of the brain for different visual stimulus categories is one of the most fascinating topics in the cognitive neurosciences. Interestingly, recent research suggests the existence of additional regions for newly acquired stimuli such as letters (letter form area; LFA; Thesen et al., 2012) and numbers (visual number form area; NFA; Shum et al., 2013). However, neuroimaging methods thus far have failed to visualize the NFA in healthy participants, likely due to fMRI signal dropout caused by the air/bone interface of the petrous bone (Shum et al., 2013). In the current study, we combined a 64-channel head coil with high spatial resolution, localized shimming, and liberal smoothing, thereby decreasing the signal dropout and increasing the temporal signal-to-noise ratio in the neighborhood of the NFA. We presented subjects with numbers, letters, false numbers, false letters, objects and their Fourier randomized versions. A group analysis showed significant activations in the inferior temporal gyrus at the previously proposed location of the NFA. Crucially, we found the NFA to be present in both hemispheres. Further, we could identify the NFA on the single-subject level in most of our participants. A detailed analysis of the response profile of the NFA in two separate experiments confirmed the whole-brain results since responses to numbers were significantly higher than to any other presented stimulus in both hemispheres. Our results show for the first time the existence and stimulus selectivity of the NFA in the healthy human brain.

SIGNIFICANCE STATEMENT This fMRI study shows for the first time a cluster of neurons selective for visually presented numbers in healthy human adults. This visual number form area (NFA) was found in both hemispheres. Crucially, numbers have gained importance for humans too recently for neuronal specialization to be established by evolution. Therefore, investigations of this region will greatly advance our understanding of learning and plasticity in the brain. In addition, these results will aid our knowledge regarding related neurological illnesses (e.g., dyscalculia). To overcome the fMRI signal dropout in the neighborhood of the NFA, we combined high spatial resolution with liberal smoothing. We believe that this approach will be useful to the broad neuroimaging community.

“Neuroimaging Evidence of a Bilateral Representation for Visually Presented Numbers” by Mareike Grotheer, Karl-Heinz Herrmann, and Gyula Kovács in Journal of Neuroscience. Published online January 6 2016 doi:10.1523/JNEUROSCI.2129-15.2016

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