Disruptions in physical substrates of vision following traumatic brain injury
Mark J. Ashley, David A. Hovda in Traumatic Brain Injury, 2017
The diencephalon is the brain region above the brain stem, and it sits deep in the midline between the cerebral hemispheres. It has two major components: the thalamus and the hypothalamus. The thalamus gates sensory input to the cerebral hemispheres and is vital for processing of the attentional system. Pertinent visually related subcortical nuclei located in the thalamus are the pulvinar and the lateral geniculate body (LGN). The pulvinar occupies 40% of the thalamic volume, is located in the posterior portion, and is considered an association nucleus involved in complex visual function. The lateral pulvinar is linked with the posterior parietal, superior temporal, and medial and dorsolateral extrastriate cortices8 as well as the superior colliculus.9 It plays a role in orientation and processing visual information in the dorsal stream. The inferior pulvinar is linked with temporal lobe areas concerned with visual feature discrimination and extrastriate areas concerned with higher analysis of vision. It also receives visual input from the superior colliculus9 in addition to direct input from the retinal ganglion cells.8 The LGN is the other thalamic visually related nucleus that is part of the afferent system. The LGN also receives projections back from cortical-related visual areas, indicating that higher cortical processing can influence visual perception at an earlier level.
The Holistic Nature of Consciousness
Max R. Bennett in The Idea of Consciousness, 2020
Francis Crick7 has suggested that the attentional mechanism for this process is centered in the thalamus. The sensory inputs to the neocortex arise from the thalamus (Figure 3.13). The principal neurons of the thalamus in turn receive connections from such sources of sensory information as the retina. The principal neurons in the thalamus are surrounded by a concentric layer of neurons called the reticular complex; this receives connections from the neocortex as well as from axons that leave the thalamus on their way to the neocortex. Most importantly, these reticular neurons make connections with the principal neurons of the thalamus that are only inhibitory. Within the thalamus itself there is another set of neurons, called the pulvinar, which also receives connections from the neocortex as well as projecting extensively to the neocortex. These pulvinar neurons, like those of the reticular complex, make inhibitory connections with the principal neurons of the thalamus. Crick has argued that if there exists consciousness of a particular aspect of the visual field then an attentional mechanism is operating that involves the reticular complex and the pulvinar. Neurons in these structures depress the sensory input from the thalamus to the neocortex that is not relevant to solving the binding problem associated with this particular aspect. The neuronal groups in the visual neocortex that are solving this problem are therefore given an excitatory advantage over those solving other binding problems.
The Pulvinar Complex
Jon H. Kaas, Christine E. Collins in The Primate Visual System, 2003
parts of the inferior pulvinar. The retinorecipient zone of PI was found to occupy roughly the part of PI adjacent to both medial geniculate nucleus (MGN) and the brachium of the superior colliculus (BrSC). Some results also suggested that the medial pulvinar (PM) receives retinal input,38 although this was not confirmed in other studies.40,41 More recently, retinal projections to the inferior pulvinar were related to pulvinar subdivisions revealed by the antibody against calbindin-D28K.42 These results confirmed the presence of a direct retinal projection to the inferior (PI), but not medial pulvinar (PM) in macaque monkeys (described by Itaya and Van Hoesen38). Generally the relative location and extent of terminals appear quite similar to previous descriptions of this retino-thalamic pathway.35,38-40 Moreover, the study revealed that the major retinal input was to the medial PI subdivision (PIm), with some involvement of the adjacent posterior and central subdivisions. These results suggest that PIm, which receives input from the retina and sends axons to visual area MT, could relay visual information from the retina to MT.42 Possibly this explains the activation of area MT neurons after V1 lesions4344× (however, see Collins et al.45).
Thalamic neuromodulation in epilepsy: A primer for emerging circuit-based therapies
Published in Expert Review of Neurotherapeutics, 2023
Bryan Zheng, David D. Liu, Brian B Theyel, Hael Abdulrazeq, Anna R. Kimata, Peter M Lauro, Wael F. Asaad
Because classification schemes based primarily on local anatomy and histology do not capture the functional heterogeneity of individual thalamic nuclei, some modern thalamic classification systems are based on circuit topology[26]. Distinctions have been made based on (i) the characteristics of thalamocortical output – core versus matrix nuclei[27], (ii) input – first- versus higher-order nuclei[28], or (iii) both input and output[29]. For example (of [i]), the anterior nucleus of the thalamus (ANT) has been defined as a core nucleus because it provides focal projections as a node in the medial limbic circuit. The pulvinar nucleus, specifically the PuM, also possesses ‘core-like’ properties based on its distinct circuits involving the temporal lobe[24]. In contrast, matrix nuclei like the centromedian nucleus of the thalamus (CMT) are characterized by markedly more diffuse cortical projections[30]. Meanwhile, within the framework of the first- and higher-order nuclear scheme (ii): first-order nuclei receive ‘driver’ inputs from subcortical sites carrying primary sensory information (e.g. lateral geniculate nucleus [LGN] receives visual input from the retina), while higher-order nuclei (e.g. the pulvinar) receive driver inputs from cortical layer V and primarily participate in transthalamic cortico-cortical circuits[28]. This classification scheme is useful in that it highlights how the thalamus continues to be involved in information processing between areas of cortex in addition to modulating and relaying primary sensory information.
Thalamocortical neural responses during hyperthermia: a resting-state functional MRI study
Published in International Journal of Hyperthermia, 2018
Jing Zhang, Shaowen Qian, Qingjun Jiang, Guanzhong Gong, Kai Liu, Bo Li, Yong Yin, Gang Sun
Additionally, the temporal-thalamic connectivity was increased in the thalamic pulvinar with the posterior inferior temporal gyrus. This finding might reflect neural activity redistribution within temporal lobe. The inferior temporal gyrus processes visual stimuli of objects in our field of vision and is associated with memory and memory recall to identify that object. It is associated with the processing and perception created by visual stimuli, comparing that processed information to stored memories of objects to identify the object [39]. Disrupted connections in the pathways might result in altered visual information perception and processing. This finding might provide potential explanations for our previous study, which declared impaired early stage of face recognition during hyperthermia [40]. Additionally, compared with the frontal-thalamic and somatomotor-thalamic connectivity, the temporal-thalamic connectivity was relatively preserved during hyperthermia. The diversity indicated hyperthermia had selective impact on cortical-thalamic pathways.
Performance of Topological Perception in the Myopic Population
Published in Current Eye Research, 2020
Yi Sun, Fei Li, Hao Li, Yunhe Song, Wenbo Wang, Rouxi Zhou, Jian Xiong, Wanbing He, Yuying Peng, Yuhong Liu, Liping Wang, Yan Huang, Xiulan Zhang
Myopia can be used as an ideal model to judge visual processing ability in pathological conditions. Previous studies have shown that the M visual pathway is affected in myopic subjects. Garcia-Domene et al. reported that the M visual pathway was affected in highly myopic eyes.14 Kuo et al described that central motion perception was reduced in subjects with HM, which is a complex visual task handled mainly through the M visual pathway.15 Given the role of the M pathway in topological perception,11 topological perception was expected to be abnormal in a highly myopic population. However, our results showed that myopic and emmetropic participants’ performances in the topological perception task were not obviously different. This seemingly paradoxical finding may be associated with the multiple functions of the M pathway.25,26 Topological perception processing may be just one function of the M pathway, and the specific function may not be impaired in myopic participants. In fact, the anatomical components of the M pathway have not yet been clearly defined, and there is limited evidence supporting the idea that topological perception is processed by the M pathway. In contrast, the relatively powerful fMRI study showed the involvement of SC-pulvinar subcortical route in processing the hole feature.13 To date, signs of impairment in subcortical pathways such as the SC-pulvinar pathway have not been reported among HM individuals. Therefore, at the beginning of the study, we speculated that the topological perception performance in HM subjects should be normal. The underlying mechanism of topological perception discrimination is not fully elucidated. Other complicated factors may be involved.
Related Knowledge Centers
- Cingulate Cortex
- Connectome
- Nucleus
- Parietal Lobe
- Visual Cortex
- Brain
- Thalamus
- Soma
- Neuron
- Two-Streams Hypothesis