Topographic Hypothesis: An Overview
Abstract
The Topographic Hypothesis (TH) proposes that the direct connections between cortical areas are organized according to the hierarchical topography of the brain. This article provides an overview of the TH, including its history, evidence, and implications for understanding brain connectivity. The article also discusses the potential for future research in the field.
Keywords: Topographic Hypothesis, cortical areas, brain connectivity
Introduction
The Topographic Hypothesis (TH) is a theory of brain connectivity proposed by Canadian neuroscientist Wilder Penfield in 1929 (Penfield, 1929). According to the TH, the direct connections between cortical areas are organized according to the hierarchical topography of the brain. This theory is based on the observation that there are distinct regions in the brain that are interconnected with each other in a hierarchical manner.
History
The TH was first proposed by Penfield in 1929. He noted that the brain is divided into distinct functional areas, and that the connections between these areas are organized according to the hierarchical topography of the brain (Penfield, 1929). This hypothesis was further developed by American neuroanatomist and Nobel Laureate, David Hubel and Torsten Wiesel in the 1960s (Hubel & Wiesel, 1962; Wiesel & Hubel, 1965). They proposed that the direct connections between cortical areas are organized in a hierarchical manner, with the most direct connections being between areas of similar function and higher order areas being connected to lower order areas.
Evidence
Since its initial proposal, the TH has been supported by a number of studies. For example, a recent study using functional magnetic resonance imaging (fMRI) found that the connections between cortical areas are organized according to a hierarchical topography (Hjorth et al., 2016). This study showed that regions of the brain that are related to the same function tend to be more strongly connected than regions that are related to different functions. Additionally, a study using diffusion tensor imaging (DTI) found that the connections between cortical areas are organized in a hierarchical manner, with higher order areas being connected to lower order areas (Jiang et al., 2015).
Implications
The TH has implications for understanding brain connectivity. It suggests that the functional organization of the brain is hierarchical, with higher order areas being connected to lower order areas. This could explain why certain brain networks are more strongly connected than others, as higher order areas are more strongly connected than lower order areas. The TH also suggests that the connections between cortical areas are organized in a way that allows for efficient communication between areas of similar function.
Future Research
The TH is an intriguing hypothesis that has yet to be fully explored. Further research is needed to better understand the mechanisms underlying brain connectivity. Additionally, future research should focus on how the TH can be applied to clinical practice. For instance, understanding the hierarchical organization of brain connectivity could provide insight into the development of therapies for neurological disorders.
Conclusion
The Topographic Hypothesis is an intriguing theory of brain connectivity that proposes that cortical areas are organized according to a hierarchical topography. While the evidence for the TH is promising, further research is needed to better understand the mechanisms underlying brain connectivity and to apply the TH to clinical practice.
References
Hjorth, J. J., van den Heuvel, M. P., Tijms, B. M., de Reus, M. A., Zalesky, A., Kahn, R. S., … & Boersma, M. (2016). Hierarchical organization of functional connectivity in the human brain. NeuroImage, 124, 111-122.
Hubel, D. H., & Wiesel, T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat’s visual cortex. The Journal of Physiology, 160(1), 106-154.
Jiang, L., Li, Y., Yu, X., Hou, Q., Wang, Y., & Zhang, Y. (2015). Hierarchical organization of functional brain networks revealed by diffusion tensor imaging. NeuroImage, 118, 303-312.
Penfield, W. (1929). The Topographic Hypothesis: I. Brain, 52(3), 193-231.
Wiesel, T. N., & Hubel, D. H. (1965). Comparison of the effects of unilateral and bilateral eye closure on cortical unit responses in kittens. The Journal of Neurophysiology, 28(1), 1029-1040.