“Sixth Sense” Discovered for Numerosity Using fMRI Scans

Sixth Sense discovered for numerosity using fMRI scanning

Scientists may have discovered a “sixth sense” that relates to something called numerosity, which involves the ability to rapidly assimilate the number of objects within one’s field of vision. The team behind the study used fMRI scans to highlight the activity of a key area of the brain, which seemed to alter its response based upon the number of objects perceived.

Dubbed a “number sense,” the phenomenon is believed to manifest in a part of the brain called the posterior parietal cortex, situated around the crown of an individual’s head.

Homunculus showing the somatosensory cortex mapping
Homunculus diagram, showing the precise somatosensory cortex mapping

The human brain is a remarkably complex organ, which researchers are still getting to grips with. We are already aware that some of the primary senses can be topographically mapped. For example, the somatosensory cortex, involved in touch, is a region of the brain where neuronal activity is specific to different parts of the body.

The diagram shows this topographical mapping for the somatosensory cortex, with localized regions of this part of the brain being responsible for sensation of different parts of the human body. This part of the brain is called the central gyrus. When receiving external electrical stimulation, at precise locations, we already know which part of the body will be sensed, based upon the constructed map.

According to the latest study, the brain might have a similar “map” for numerosity. A particular area of neurons, within the posterior parietal cortex, became activated when people were presented with different numbers of objects.

The study’s lead researcher, Ben Harvey, who works at the Utrecht University in the Netherlands, explained that most people don’t need to methodically count a small number of objects presented to them, “… we just know how many there are straight away.” This has led many people to maintain that a person’s numerosity powers represent something akin to a “sixth sense.”

The study went on the auspices that such a map could exist. Therefore, the group decided to perform this “mapping,” using a functional magnetic resonance imaging (fMRI) scanner. fMRI scanners measure the patterns of bloodflow to particular regions of the brain, relying upon the difference in magnetization between oxygen-rich and oxygen-poor blood. Delivery of an oxygen-rich blood supply, to a given area, indicates a highly metabolically active part of the brain.

A topographical map was then generated to demonstrate the researcher’s results. Areas that were stimulated by a particular number of dots were then color-coded.

The team presented participants with a series of dots, repeatedly. For example, one dot would be shown over and over, and the resultant pattern of bloodflow would then be measured. The same procedure would be conducted for two dots, and so on.

The pattern of bloodflow suggested different regions of the posterior parietal cortex responded to the different numbers of dots in unique ways. Essentially, regions of the posterior parietal cortex showed varying levels of activity, dependent upon the number of dots that were presented.

Topographic Map of the posterior pareital cortex for numerosity
Topographic map of the posterior parietal cortex, involved in numerosity. Areas are color-coded to indicate region-specific activation when subjects were presented with different numbers of dots.

The group found that number sensing in humans is limited, however. Small numbers of objects are readily detected, whereas larger numbers of items are much more difficult to handle. As is evident from the topographical map, vast areas of the posterior parietal cortex were dedicated to interpreting numerosity involving a smaller number of objects. The presentation of three to four dots seemed to result in the greatest activity throughout this area of the cerebral cortex.

One of the lead authors on the study explained that everybody is different; some people have better numerosity skills than others. This same variation is witnessed when investigating difference in aptitude for other skills, including mathematics and literature. For example, some individuals who fall on the autistic scale have extraordinarily abilities in mathematics, but may be less capable in other areas.

During a recent press release, Harvey discussed some of the findings and implications of his study:

“I was very surprised then that the map we report is in such a consistent location between our subjects, and that numerosity preferences always increased in the same direction along the cortex… the extent of individual differences … is also striking.”

According to Harvey, during his study, one of the subject’s brains “responded” to eight dots, during fMRI scanning, highlighting the range in numerosity ability that exists between different people. Overall, it seems the “sixth sense” has a topographical mapping that is not too dissimilar to that of other primary senses, such as vision and touch.

By: James Fenner

Press Release Link

Science Journal Source

NPR News Link

2 Responses to "“Sixth Sense” Discovered for Numerosity Using fMRI Scans"