Annectant Gyri in Parietal Cortex Capture Dorsal Visual Stream Boundaries

2133 

Abstract Submission 

Anna Lyn Williams¹, Patricia Hoyos¹, Ruggaya Musa¹, Edan Daniel-Hertz¹, Na Yeon Kim², Jesse Gomez¹

¹Princeton University, Princeton, NJ, ²California Institute of Technology, Pasadena, CA

Anna Lyn Williams  
Princeton University
Princeton, NJ

Patricia Hoyos  
Princeton University
Princeton, NJ

Ruggaya Musa  
Princeton University
Princeton, NJ

Edan Daniel-Hertz  
Princeton University
Princeton, NJ

Na Yeon Kim, PhD  
California Institute of Technology
Pasadena, CA

Jesse Gomez, PhD  
Princeton University
Princeton, NJ

Visual processing is separated into the ventral and dorsal streams, responsible for object recognition and spatial attention. While functional boundaries of the ventral stream have been linked to cortical folding (Witthoft et al. 2014), no such model exists for the dorsal stream. Unlike the ventral stream, most of the dorsal stream's maps exist within one continuous sulcus, the paraoccipital sulcus (PO) into the intraparietal sulcus (IPS). However, the field lacks a definition of intrasulcal anatomical features that could enhance our understanding of this region's structural relationship to function.
Our study explores annectant, or concealed, gyri within the PO sulcus, building on Gratiolet's 1854 findings of buried gyri within the macaque brain. We hypothesize that there are consistent annectant gyri across the dorsal stream which overlap with dorsal stream visual field map boundaries. If structure and function are coupled in the dorsal stream, we also hypothesize that variability in PO anatomy can be related to behavioral measures such as visuospatial bias (VSB).

Employing anatomical and functional MRI, we collected data from 20 adults (mean age 33 ± 15). An average of 3.0 (± 0.4) annectant gyri were identified in the left PO and 3.2 (± 0.8) in the right. These hidden gyri are consistent to the extent that three annectant gyri in the left PO and two in the right remain visible in cortical surface averages from FreeSurfer and Human Connectome Project participants (Fischl et al., 1999). Annectant gyri extend perpendicularly across PO and IPS, and were distinguished based on their spatial positioning relative to other sulcal landmarks, such as the transverse occipital sulcus and parieto-occipital fissure. Specifically, four annectant gyri were consistently identified to overlap with retinotopically defined left hemisphere dorsal stream map boundaries in over 80% of participants for V3ab/IPS0 (89%), IPS0/IPS1 (89%), IPS1/IPS2 (83%), and IPS2/IPS3 (83%). Some of these annectant gyri partially extend across the PO sulcus, while others fully interrupt the continuity of the sulcus.

We also investigated how structure-function couples to behavior, using anatomical MRI data and VSB scores from a cohort of 38 children (mean age 10 ± 2). In each child we quantify the surface area and gray matter volume of the PO sulcus in each hemisphere and derive a normalized anatomical bias score (left - right)/(left+right). Subsequently, children were stratified into two groups based on their VSB scores relative to the median, distinguishing those with strong leftward and weak rightward spatial biases. Results indicated that individuals with a pronounced rightward VSB exhibited a notable leftward bias in cortical surface area (t-stat=2.1, p=0.047) and gray matter volume (t-stat=2.2, p=0.039). This relationship was specific to PO and not observed in other sulci such as the central sulcus.
To further examine development, in a subset of participants with both retinotopic mapping and structural imaging (n=18 adults; n= 7 children), we find left hemisphere predominance in surface area (p = 0.029), gray matter volume (p = 0.001), and cortical thickness (p = 1x10-06) in PO and IPS, the two sulci that contain retinotopic dorsal stream visual field maps, indicating ongoing cortical folding in the dorsal stream into adulthood. These results suggest a protracted development of the left relative to the right parietal cortex, consistent with the rightward shift of VSB throughout development.

Our findings reveal novel and consistent anatomical features in the parietal lobe, and suggest that dorsal visual stream organization can be predicted from cortical sheet folding. Establishing criteria for intrasulcal anatomical features can enrich analyses in populations where retinotopy data cannot be collected. The developmental dynamics observed warrant further exploration to understand the interplay between structure, function, and cognitive functions of the dorsal stream.

Early life, Adolescence, Aging

Anatomy and Functional Systems

Cortical Anatomy and Brain Mapping ¹

Brain Atlases

Attention: Visual ²

Cognition

Cortex

Development

FUNCTIONAL MRI

Hemispheric Specialization

MRI

Perception

Vision

Other - Anatomy