Touch Sensation and Brain Activity Studied Between Couples Using FMRI

Highlights:

Two-person fMRI can be used to study social interaction between two individuals
The interaction mediated through touch can be studied by recording brain activity
The technique could be instrumental in explaining the neurological basis of socio-cognitive communication

Tactile interaction between two persons can now be imaged in real-time by functional magnetic resonance imaging (fMRI), reveals a new study conducted jointly by scientists at Aalto University School of Science, Espoo and the University of Turku, Finland. The study was led by Dr. Lauri Nummenmaa, who is a Professor at the Turku PET Center and Department of Psychology, University of Turku, Turku, Finland.

Most studies on brain imaging, scan the brain wave patterns of subjects individually. In the case of social interaction, studying the brain wave patterns requires that the two persons should be in contact with each other, while their brain activities are recorded. Most importantly, the brain activities of the two interacting individuals need to be measured simultaneously instead of individually. This poses a huge challenge for scientists and has not been possible, until now.

‘Touch sensation exchange between two persons can be studied by simultaneously measuring brain activity using fMRI, which shows how social interaction occurs in real-time.’
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Uniqueness of the Study

This study is the very first proof-of-concept demonstration of measurement of the brain activities of two interacting individuals, mimicking social interaction through the sensation of touch. The uniqueness of the study lies in the fact that the brain wave patterns of the two interacting individuals were recorded simultaneously within the bore of a single MRI scanner.

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Study Technique

The study involved a special type of imaging technique known as two-person blood oxygenation dependent fMRI imaging (BOLD-fMRI). As opposed to a standard 32-channel head coil, a customized 16-channel (8 + 8 channels) two-helmet coil was developed so that these could be worn by both the individuals for simultaneously measuring their brain activities during tactile interaction.

The detailed methodology is highlighted below:

The study involved 10 pairs or 20 subjects (7 male-female pairs; 3 female-female pairs)
The average age of the subjects was 23 ± 3 years
All the pairs were friends or romantic partners
All the subjects were right-handed
None of the subjects had any history of neurological illness
All the subjects were screened for MRI exclusion criteria before scanning
A 3-T whole body MRI system was used to acquire the following types of images:

Anatomical images
Resting state scans
Task-based fMRI

The subjects lay parallel to each other within the bore of the MRI scanner
The subjects shared the same physical space with a realistic face-to-face contact
Touching was used as the model task to convey affection and trust in a social context
The subjects tapped each other’s lips and their feelings were reflected in the alteration of their brain wave patterns

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Study Findings

Vocal cues generated by either subject at the beginning of every ‘rest’ and ‘task’ command elicited bilateral activation of their auditory cortex (region of the brain responsible for hearing)
Touching tasks led to differential activation of the sensory cortex (region of the brain that receives impulses to generate sensations) or motor cortex (region of the brain that sends impulses for the execution of movements), depending on whether the subject was receiving taps or was tapping

Interpretation of the Study Findings

The study clearly shows that hemodynamic activity can be effectively measured from the brains of two interacting individuals wearing dual helmet coils and positioned within a single MRI scanner. The study indicates that the two-person fMRI recordings are instrumental for studying elementary socio-cognitive functions, such as interpersonal communication mediated through the sensation of touch.

Limitations of the Study

The fMRI scanner had moderate image resolution capacity that produced images of suboptimal quality and was not totally suitable for the two-person MRI set-up
The coil coverage of the scalp was not maximized or evenly distributed, thereby generating feeble and incoherent signals
The signal-to-noise ratio (SNR) was far inferior to that of a standard 32-channel head coil

In conclusion, the two-person fMRI is a useful, potentially powerful and robust technology that allows the study of brain patterns during real-time social interaction between two persons. The only drawback is that the signal quality is relatively poor compared to state-of-the-art 32-channel head coils. Nevertheless, this proof-of-concept study clearly establishes that it is possible to collect good quality hemodynamic signals simultaneously from two brains using a single MRI scanner.

Funding Source

The study was funded by the Swedish Cultural Foundation in Finland, the Instrumentarium Science Foundation, the Kalle and Dagmar Välimaa Fund of the Finnish Cultural Foundation, the Academy of Finland and the European Research Council.

Reference:

Imaging Real-Time Tactile Interaction with Two-Person Dual-Coil fMRI - bioRxiv, Cold Spring Harbor Laboratory, New York, USA - (https://www.biorxiv.org/content/10.1101/861252v2.full)

Source-Medindia