This study sought to understand how the brain interprets numbers, including symbolic and non-symbolic, which helps to understand cognitive development. Earlier research indicates that humans and other animals have a non-symbolic number sense, but symbolic representations are obtained culturally and exclusive to humans only. This study used multivariate analysis and functional magnetic resonance imaging (fMRI) for a complete examination of these processes.
Neuroimaging studies show that the voluntary motions of virtual fingers activate brain patterns that are the same as those of people with normal bodies. These investigations have provided proof, but they are unable to determine if the virtual hand or face mappings were preserved in comparison to pre-amputation form. Three adult participants had their face (lips) and hand cortical representations tracked using an fMRI technique up to five years after arm amputation. To monitor the development of cortical representations before and after amputation.
Over six months, researchers examined 16 able-bodied individuals at four time points and three adult amputees at four to five time points. The remaining contractions of the limb muscles during phantom motions further validated motor control over the virtual hand. Phantom activity matched the amplitude and spatial activity distribution of pre-amputation activity. While individual finger activity and projecting hand throughout the somatosensory cortex (S1) shows steady activity before and after amputation.
At six months, multivoxel activity patterns of pre-amputation and virtual finger representations showed a strong correlation. The research suggests that regenerative peripheral nerve terminals and targeted muscle do not reverse reorganization or change the cortical hand representation in the treatment of phantom limb pain. 180 people in three age groups participated, including children between 6 and 9 years old, teenagers between 12 and 15 years old, and adults between 18 and 27 years old. Neural activity patterns in various brain areas were decoded using representational similarity analysis (RSA) and multivoxel pattern analysis.
The symbolic and non-symbolic numbers produced different patterns of brain activity. The early visual and parietal regions were strongly activated by non-symbolic numbers, while ventral temporal regions and left-lateralized language were dependent on symbolic numbers. The developmental shift in children shows strong and reliable representations of non-symbolic numbers with weak symbolic representations.
In adolescents, it shows a growing overlap in representation between non-symbolic and symbolic numbers. In adults, it shows strong and symbolic number representations that closely match non-symbolic representations. Successful transmission between symbolic and non-symbolic numbers was noted by adults but not by children, as per cross-classification studies. As age increases, symbolic number processing was observed in the left ventral temporal cortex and language-related regions. There was a correlation between abilities and the quality of the symbolic number representation of participants.
Initially, symbolic numbers were scattered and represented weakly, but with experience and learning, they align with non-symbolic representations. This study highlighted that the human brain represents numbers in both symbolic and non-symbolic formats with developmental integration. Adults achieve substantial symbolic to non-symbolic integration, teenagers show increased overlap, while children depend mostly on non-symbolic representations. The symbolic numbers gain meaning by connecting with non-symbolic representations to support the developmental process.
Reference: Schone HR, Maimon-Mor RO, Kollamkulam M, et al. Stable cortical body maps before and after arm amputation. Nat Neurosci. 2025. doi:10.1038/s41593-025-02037-7
