Der Entwicklungsprozess von nicht evolutionär angelegten Verarbeitungsregionen im menschlichen Gehirn
Zusammenfassung der Projektergebnisse
Math and reading skills are essential in our everyday lives. We are not born with these uniquely human abilities, but rather acquire them through extensive training, typically during childhood development. Surprisingly, in adulthood, the human brain contains neural substrates specialized in supporting math and reading, including regions in the visual system that are preferentially involved in processing numbers or letters. Math and reading further have both shared, e.g. encoding of visual stimuli, as well as dissociated, e.g. quantity processing, cognitive components. Hence, it is likely that these skills utilize both shared and dissociated neural substrates, which are unknown to date. Here, we addressed this fundamental gap in knowledge in the visual system, by evaluating if regions involved in processing numbers and letters are segregated or overlapping. This overall goal was reached by fulfilling two objectives: 1) determine if there is spatial overlap between regions involved in processing numbers and letters and 2) evaluate the impact of math and reading tasks on neural responses in these regions. Our results show that regions involved in processing numbers (ITG- numbers) and letters (OTS-letters, also referred to as the visual word form area are neighboring but not overlapping in cortex. Strikingly, our data further reveal that the performed task has a dramatic impact on the responses of these regions. During a 1-back task, ITG-numbers and OTS-letters showed the expected preferences for numbers and letters, respectively. However, during math or reading tasks, ITG-numbers and OTS-letters responded equally strongly to number-letter morph stimuli that contain either >80% number or >80% letter information. One may argue that this lack of preference is due to the visual similarity of number-letter morphs. However, for ITG-numbers, we replicated this observation using visually dissimilar stimuli. That is, we also showed that, during a math task, ITG-numbers responds equally strongly to numbers, dice and hands. Therefore, our data provide compelling evidence that ITG-numbers is involved in extracting numerical value from the visual input, irrespective of the format of the stimuli. Towards the end of the funding period, we extended these investigations to the whole brain level and determined what are shared and dissociated gray and white matter substrates of the math and reading networks (Grotheer et al., in revision). In an innovative, multimodal approach, that combines functional MRI, diffusion MRI, and quantitative MRI, we first defined these networks and then evaluated structural properties of their fascicles. Results reveal that math and reading are processed in parallel in the adult human brain. First, neighboring gray matter regions are involved in processing one task or the other. Further, while the superior longitudinal (SLF) and arcuate (AF) fascicles are involved in both math and reading networks, within these fascicles, reading- and mathrelated tracts are segregated into parallel sub-bundles. Strikingly, our qMRI data further revealed that tracts associated with reading show faster T1 relaxation, which indicated a higher degree of myelination, compared to tracts associated with math. Overall, these results significantly advance our understanding of the neural substrates of math and reading, two fundamental skills learned by children world-wide. Our data reveal that, even though math and reading involve several shared cognitive components, such as the encoding of visual stimuli, they are processed largely in parallel in the human brain. This, in turn, suggests that improvements in one skill may not translate to the other skill, unless this improvement is linked to broad changes that transcend entire fascicles. Further, since reading is practiced more intensely than math during childhood, and myelination is dependent on neural activity, our data provide important evidence for the intriguing prediction that the amount of learning and its resultant neural activity may affect the myelination of specific white matter tracts within fascicles. Finally, our data may simultaneously explain both isolated and comorbid cases of math and reading learning disabilities, as these may be associated with white matter abnormalities within sub-bundles or entire fascicles, respectively.
Projektbezogene Publikationen (Auswahl)
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(2017). A preference for mathematical processing outweighs the selectivity for Arabic numbers in the inferior temporal cortex. SFN Abstract Supplement, contribution 403.27
Grotheer, M., Jeska, B., & Grill-Spector, K.
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(2018) A preference for mathematical processing outweighs the selectivity for Arabic numbers in the inferior temporal gyrus. Neuroimage, 175:188–200
Grotheer, M., Jeska, B., Grill-Spector, K.
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(2018). A preference for mathematical processing outweighs the selectivity for Arabic numbers in the inferior temporal cortex. VSS Abstract Supplement, contribution 35.23
Grotheer, M., Jeska, B., & Grill-Spector, K.
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Separate lanes for math and reading in the white matter highways of the human brain
Grotheer, M., Zhen, Z., & Grill-Spector, K.
