Integrating Anatomy and Physiology of the Primary Visual Pathway: From LGN to Cortex

Abstract

This chapter deals with the structure and function of the visual thalamus (lateral geniculate nucleus, LGN) and the primary visual cortex and aims to put this system into a computational perspective. We start with an overview of the basic structures of the primary visual pathway and the terminology used. Next, the organization of the LGN and its main functions are described: receptive field structure of LGN cells, excitatory and inhibitory influences, contrast gain-control, spatial summation, temporal structure of activity and influence of extra-retinal inputs. The section closes with models on three functional aspects of the LGN: 1) Switching between burst firing and tonic transmission modes of LGN cells, 2) Control of LGN function during the sleep-wake cycle, and 3) Involvement of LGN in gating visual signals. The section on the visual cortex starts with details of its morphological organisation: cortical layers, cell types, columnar structure and horizontal connections. This is followed by a description of the basic response characteristics of neurons, the organisation of receptive fields and their dynamic behavior. Here, mechanisms of establishing cortical orientation selectivity are considered in detail. Next, we focus on functional maps, e.g. distribution of orientation preferences of cells. The chapter closes with a section on basic models of the primary visual cortex, concerning: 1) Temporal firing patterns of neuronal assemblies, i.e. oscillations and synchronization, 2) Cortical cell characteristics, e.g. orientation specificity, and 3) Formation of functional maps, e.g. orientation map. J. L. van Hemmen et al. (eds.), Models of Neural Networks IV

A spherical model for orientation and spatial–frequency tuning in a cortical hypercolumn

“…Our suggestion regarding the function of the corticogeniculate feedback pathway differs considerably from many others. These other proposals have been concerned with such functions as gating retino-geniculate transmission, improving the precision of spike timing in LGN cells, enhancing the spatial-frequency tuning of LGN cells, and synchronizing slow oscillations between V1 and LGN (see Funke et al 2001). Our model is closest in concept to that of Rao & Ballard (1999) who suggested that in general, feedback connections carry predictions of lower level activities, whereas the corresponding feed-forward connections carry the residual errors between the predictions and the actual lower level activities.…”

Functional and Neural Mechanisms of Out-of-Body Experiences: Importance of Retinogeniculo-Cortical Oscillations

“…Current research points to pathological issues, such as dysfunction within the temporo-parietal cortex, as common factors in various autoscopic phenomena[26], but evidence of the reticular thalamic nucleus and retinogeniculo-cortical oscillatory activity and their role in these phenomena is absent in the literature. For example, the lateral geniculate body is involved in visuospatial perception, attention, and vision[42] [43], and the medial geniculate body is involved in establishing body position and location[44], yet there is no discussion in the literature of the roles of thalamic nuclei in autoscopic phenomena.Furthermore, without investigation into and understanding about how normal intraand extrapersonal space is perceived in cases of various autoscopic phenomena, clinical conditions cannot be fully explained. If the thalamus is a central hub that integrates visual and vestibular information, along with consciousness of the "self", then it is reasonable to consider that focused research on the reticular thalamic nucleus and the retinogeniculo-cortical oscillations could offer insight into how various autoscopic phenomena occur.…”