Posterior Collateral Sulcus Research Articles

COLLATERAL SULCUS MORPHOLOGY IN NORMAL INDIVIDUALS IN MAGNETIC RESONANCE IMAGING OF BRAIN

Collateral sulcus (CS) develops during early stage of the gestation and is well formed at 23rd weeks during pregnancy. The temporal part of the CS continues with limbic ssure and forms a cortical fold. This folding creates a protrusion inside the temporal horn of the lateral ventricle that is named the collateral eminence. The occipital part of CS, which is named as the posterior transverse CS, forms a border between the lingual gyrus and lateral occipitotemporal gyrus. The CS and the occipitotemporal sulcus (OTS) are the prominent landmarks that separate the mesial and lateral temporal lobe. Collateral sulcus angle and depth are used as indirect criteria to look for presence or absence of incomplete hippocampal inversion. AIM: To describe the normal morphological patterns of collateral sulcus in magnetic resonance imaging of brain. OBJECTIVES: 1. To document the range, mean, SD of depth of the collateral sulcus. 2. To determine the collateral sulcus angle range, mean, SD in normal MRI brain. Materials and Methods: A retrospective and prospective observational study was conducted in a tertiary centre using T1 3D MRI images of brain morphological pattern of collateral sulcus in normal individuals for whom MRI brain was normal otherwise was recorded. The MRI images of a total of 250 individuals qualied for the study. Collateral sulcus angle was calculated angle between line drawn horizontal and along depth of collateral sulcus. Results: We arrived at normal distribution of collateral sulcus angle and the mean Collateral Sulcus Angle Degree of the studied patients (N=250) on Right side was recorded as 38.66 degrees with standard deviation of 10.811 degrees. The mean Collateral Sulcus Angle Degree of the studied patients (N=250) on left side was recorded as 42.11 degrees with standard deviation of 13.09 degrees. In current study, we have observed that in all patients with collateral sulcus angle >65 degrees, depth of the collateral sulcus of the corresponding side is </= 7mm. (Mean collateral sulcus depth on right side is 10.1mm and on left side is 10.3mm). Vertical collateral sulcus (> 70 degree from horizontal) and near vertical collateral sulcus (65degree to 70 degree) are observed even with normally appearing properly inverting hippocampus. (Such verticality being possible by shallow depth (as observed in our study) of those collateral sulci). Conclusion: Since collateral sulcus angle and depth are used as indirect criteria to look for presence or absence of incomplete hippocampal inversion, we tried to establish their normal range, mean and SD in 250 normal MRI Brains. We found an abnormal collateral sulcus angle (>70 degrees) in one normal MRI brain study out of 250 study population. Vertical collateral sulcus can be seen as an isolated nding without incomplete hippocampal inversion especially if the collateral sulcus is of shallow depth.

Large-scale dissociations between views of objects, scenes, and reachable-scale environments in visual cortex

Space-related processing recruits a network of brain regions separate from those recruited in object processing. This dissociation has largely been explored by contrasting views of navigable-scale spaces to views of close-up, isolated objects. However, in naturalistic visual experience, we encounter spaces intermediate to these extremes, like the tops of desks and kitchen counters, which are not navigable but typically contain multiple objects. How are such reachable-scale views represented in the brain? In three human functional neuroimaging experiments, we find evidence for a large-scale dissociation of reachable-scale views from both navigable scene views and close-up object views. Three brain regions were identified that showed a systematic response preference to reachable views, located in the posterior collateral sulcus, the inferior parietal sulcus, and superior parietal lobule. Subsequent analyses suggest that these three regions may be especially sensitive to the presence of multiple objects. Further, in all classic scene and object regions, reachable-scale views dissociated from both objects and scenes with an intermediate response magnitude. Taken together, these results establish that reachable-scale environments have a distinct representational signature from both scene and object views in visual cortex.

Mapping the Scene and Object Processing Networks by Intracranial EEG.

Human perception and cognition are based predominantly on visual information processing. Much of the information regarding neuronal correlates of visual processing has been derived from functional imaging studies, which have identified a variety of brain areas contributing to visual analysis, recognition, and processing of objects and scenes. However, only two of these areas, namely the parahippocampal place area (PPA) and the lateral occipital complex (LOC), were verified and further characterized by intracranial electroencephalogram (iEEG). iEEG is a unique measurement technique that samples a local neuronal population with high temporal and anatomical resolution. In the present study, we aimed to expand on previous reports and examine brain activity for selectivity of scenes and objects in the broadband high-gamma frequency range (50–150 Hz). We collected iEEG data from 27 epileptic patients while they watched a series of images, containing objects and scenes, and we identified 375 bipolar channels responding to at least one of these two categories. Using K-means clustering, we delineated their brain localization. In addition to the two areas described previously, we detected significant responses in two other scene-selective areas, not yet reported by any electrophysiological studies; namely the occipital place area (OPA) and the retrosplenial complex. Moreover, using iEEG we revealed a much broader network underlying visual processing than that described to date, using specialized functional imaging experimental designs. Here, we report the selective brain areas for scene processing include the posterior collateral sulcus and the anterior temporal region, which were already shown to be related to scene novelty and landmark naming. The object-selective responses appeared in the parietal, frontal, and temporal regions connected with tool use and object recognition. The temporal analyses specified the time course of the category selectivity through the dorsal and ventral visual streams. The receiver operating characteristic analyses identified the PPA and the fusiform portion of the LOC as being the most selective for scenes and objects, respectively. Our findings represent a valuable overview of visual processing selectivity for scenes and objects based on iEEG analyses and thus, contribute to a better understanding of visual processing in the human brain.

The role of apparent size in building- and object-specific regions of ventral visual cortex

Images of buildings and manipulable objects have been found to activate distinct regions in the ventral visual pathway. Yet, many non-categorical properties distinguish buildings from common everyday objects, and perhaps the most salient of these is size. In this fMRI study, we investigated whether or not changes in perceived scale can account for some of the differences in category-specific responses, independent of the influence of semantic or retinotopic image properties. We used independent scans to localize object-specific ROIs in lateral occipital cortex (LO) and scene-specific ROIs in the parahippocampal place area (PPA) and posterior collateral sulcus. We then contrasted the effects of stimulus category and perceived size/distance in these regions in a factorial design. Participants performed an oddball detection task while viewing images of objects, buildings, and planar rectangles both with and without a background that indicated stimulus size/distance via simple pictorial cues. The analyses of fMRI responses showed effects of perceived size/distance in addition to effects of category in LO and the PPA. Interestingly, when simple rectangles were presented in a control condition against the background that indicated size/distance, LO in the right hemisphere responded significantly more to the small/close rectangles than to the large/far ones, in spite of the fact that the rectangles themselves were identical. These findings suggest that ventral stream regions that show category specificity are modulated by the perceived size and distance of visual stimuli.

Separate Channels for Processing Form, Texture, and Color: Evidence from fMRI Adaptation and Visual Object Agnosia

Previous neuroimaging research suggests that although object shape is analyzed in the lateral occipital cortex, surface properties of objects, such as color and texture, are dealt with in more medial areas, close to the collateral sulcus (CoS). The present study sought to determine whether there is a single medial region concerned with surface properties in general or whether instead there are multiple foci independently extracting different surface properties. We used stimuli varying in their shape, texture, or color, and tested healthy participants and 2 object-agnosic patients, in both a discrimination task and a functional MR adaptation paradigm. We found a double dissociation between medial and lateral occipitotemporal cortices in processing surface (texture or color) versus geometric (shape) properties, respectively. In Experiment 2, we found that the medial occipitotemporal cortex houses separate foci for color (within anterior CoS and lingual gyrus) and texture (caudally within posterior CoS). In addition, we found that areas selective for shape, texture, and color individually were quite distinct from those that respond to all of these features together (shape and texture and color). These latter areas appear to correspond to those associated with the perception of complex stimuli such as faces and places.

Separate Processing of Texture and Form in the Ventral Stream: Evidence from fMRI and Visual Agnosia

Real-life visual object recognition requires the processing of more than just geometric (shape, size, and orientation) properties. Surface properties such as color and texture are equally important, particularly for providing information about the material properties of objects. Recent neuroimaging research suggests that geometric and surface properties are dealt with separately within the lateral occipital cortex (LOC) and the collateral sulcus (CoS), respectively. Here we compared objects that differed either in aspect ratio or in surface texture only, keeping all other visual properties constant. Results on brain-intact participants confirmed that surface texture activates an area in the posterior CoS, quite distinct from the area activated by shape within LOC. We also tested 2 patients with visual object agnosia, one of whom (DF) performed well on the texture task but at chance on the shape task, whereas the other (MS) showed the converse pattern. This behavioral double dissociation was matched by a parallel neuroimaging dissociation, with activation in CoS but not LOC in patient DF and activation in LOC but not CoS in patient MS. These data provide presumptive evidence that the areas respectively activated by shape and texture play a causally necessary role in the perceptual discrimination of these features.

Occipital sulci of the human brain: Variability and probability maps

The morphological variation of the sulci of the occipital region of the human brain was examined in both the left and the right hemispheres in 40 normal adult human brains on magnetic resonance images. We identified the occipital sulci and marked their corresponding gray matter voxels on the magnetic resonance images, which had been transformed into the Montreal Neurological Institute standard proportional stereotaxic space in order to construct probability maps. In the medial occipital region, the calcarine sulcus was the longest and most constant sulcus. We identified, in the inferior part of the medial occipital lobe, the lingual sulcus and the posterior collateral sulcus, and, in the superior part, the inferior and superior sagittal sulci of the cuneus. On the lateral surface of the occipital lobe, the lateral occipital, the lunate, and the transverse and inferior occipital sulci were identified. The parieto-occipital fissure and the temporo-occipital incisure were also identified on the lateral and medial surfaces. Finally, the patterns of the occipital sulci and gyri were examined in 20 post-mortem human hemispheres fixed in formalin. Probability maps of the occipital sulci were constructed, which provide a quantitative description of the variability of the sulci in standard stereotaxic space and may be used to identify the location of voxels in other magnetic resonance images transformed into the same streotaxic space. These maps are a useful tool in the study of functional activations related to visual processing.

Spatial memory deficits in patients with lesions to the right hippocampus and to the right parahippocampal cortex

Spatial memory tasks, performance of which is known to be sensitive to hippocampal lesions in the rat, or to medial temporal lesions in the human, were administered in order to investigate the effects of selective damage to medial temporal lobe structures of the human brain. The patients had undergone thermo-coagulation with a single electrode along the amygdalo-hippocampal axis in an attempt to alleviate their epilepsy. With this surgical technique, lesions to single medial temporal lobe structures can be carried out. The locations of the lesions were assessed by means of digital high-resolution magnetic resonance imaging and software allowing a 3-D reconstruction of the brain. A break in the collateral sulcus, dividing it into the anterior collateral sulcus and the posterior collateral sulcus is reported. This division may correspond to the end of the entorhinal\\perirhinal cortex and the start of the parahippocampal cortex. The results confirmed the role of the right hippocampus in visuo–spatial memory tasks (object location, Rey–Osterrieth Figure with and without delay) and the left for verbal memory tasks (Rey Auditory Verbal Learning Task with delay). However, patients with lesions either to the right or to the left hippocampus were unimpaired on several memory tasks, including a spatial one, with a 30 min delay, designed to be analogous to the Morris water maze. Patients with lesions to the right parahippocampal cortex were impaired on this task with a 30 min delay, suggesting that the parahippocampal cortex itself may play an important role in spatial memory.