Original ArticleAnatomy and White Matter Connections of the Lingual Gyrus and Cuneus
Introduction
The basic and complex visual processing in the primary visual area (V1) in the occipital lobe is sent to the extrastriate visual areas (V2-V4) and then to the adjacent cortices in dual, parallel streams.1 The dorsal stream extends from V1 to the posterior parietal area and facilitates visuospatial coordination. The ventral stream extends from V1 to the temporal cortex to facilitate object recognition.2 V1 surrounds the calcarine sulcus on the medial aspect of the occipital lobe, which is composed of the cuneus and lingual gyrus. More broadly, the cuneus and lingual gyri house functional areas of V1 to V4 and facilitate proper functioning of the ventral and dorsal streams.3,4 These two gyri have been implicated in both the basic and the higher order visual processing required for the orientation and direction of stimuli,5 color,6 and faces.7
Preservation of the cortical tracts originating from the medial occipital lobe and extending to adjacent cortices is essential to maintain basic visual processing in patients after cerebral surgery.8,9 Numerous studies have also suggested a possible “supramodal” organization of the brain in which the primary cortices are dependent on functional specialization rather than on unimodal sensory information alone. In line with these observations, the lingual gyrus and cuneus have also demonstrated functional relevance in processes that included visual memory storage,10 visual imagery,11 creative thinking,12 and linguistic processing.10,13 Thus, clarification of the fiber bundle anatomy of the medial occipital lobe and its connections to the adjacent cortical regions could provide insight into the underlying complex processes supported by this region and also improve our ability to apply effective intraoperative brain mapping in the occipital lobe to reduce neurologic deficits and improve patients' quality of life.14,15
In the present study, we used diffusion spectrum imaging (DSI)-based tractography to study the structural organization and connectivity of the medial occipital lobe white matter tracts with our regions of interest (ROIs) as the lingual gyrus and cuneus. Tractography was performed using generalized q-sampling imaging (GQI) validated by gross anatomic dissection performed on 10 healthy, human brains, as previously reported.16 An extensive literature review was also performed to elucidate the major functions facilitated by this cortex in the context of the network connectivity described in the present study. We have described our structural analysis of the medial occipital lobe according to the major connections and relations to other cortical structures to suggest how its connectivity might suggest function.
Section snippets
Defining the ROIs
From an anatomical perspective, the lingual gyrus was named because of its resemblance of its shape to a tongue. It is located on the posteroinferior portion of the medial surface of the occipital lobe, reaching the occipital pole. It is bound by the calcarine fissure and posterior portion of the collateral sulcus. It courses anteriorly and merges with the parahippocampal gyrus at the tentorial surface of the temporal lobe (Figure 1).
The cuneus is also located on the medial surface of the
U-Shaped Fibers
U-shaped fibers are ubiquitous between adjacent gyri. Starting from the posterior portion of the lateral aspect of the gyrus, at the collateral sulcus, the expected connections were found between the lingual gyrus and the adjacent fusiform gyrus. These fibers take an inverted U-shape. They start at the inferior aspect of the posterolateral portion of the lingual gyrus, loop upward around the collateral sulcus, and end in the medial portion of the fusiform gyrus.
These U-shaped fibers are also
Discussion
In the present study, we have demonstrated the underlying cortical anatomy of the medial occipital lobe, a region of the cerebral cortex that holds the cuneus and lingual gyrus and facilitates visual processing.5 Although functional information is beneficial to understanding the neural basis of complex behaviors such as selective object recognition,21 additional information is necessary to understand the cortical anatomy of the medial occipital lobe and its clinical relevance to cerebral
Conclusions
The medial occipital lobe has functional areas that have been linked to receiving inputs from the visual field and performing basic visual processing functions. Using DSI-based tractography, with the findings validated by those from gross dissection, we demonstrated the extent of the local interconnectedness of this portion of the occipital lobe. We demonstrated that many long range association fibers are present that might interact with visual processing to subserve semantic memory and
CRediT authorship contribution statement
Ali H. Palejwala: Writing - original draft, Investigation. Nicholas B. Dadario: Writing - original draft, Formal analysis. Isabella M. Young: Writing - review & editing, Visualization. Kyle O’Connor: Investigation. Robert G. Briggs: Methodology. Andrew K. Conner: Writing - review & editing. Daniel L. O’Donoghue: Investigation, Visualization. Michael E. Sughrue: Conceptualization, Supervision.
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.