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Anatomy and Function of Higher-order Thalamocortical Circuits in the Visual System

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Release : 2023
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Book Synopsis Anatomy and Function of Higher-order Thalamocortical Circuits in the Visual System by : Rachel M. Cassidy

Download or read book Anatomy and Function of Higher-order Thalamocortical Circuits in the Visual System written by Rachel M. Cassidy. This book was released on 2023. Available in PDF, EPUB and Kindle. Book excerpt: One of the fundamental jobs of the brain is to transform stimuli from the external environment into flexible behavioral outputs. In mammals, thalamocortical circuits perform many of the functions that underlie this complex sensory processing. First-order (FO) thalamic nuclei, such as the dorsal lateral geniculate nucleus (dLGN), relay incoming signals to the cortex, which generates a percept and motor commands. This initial path from the FO thalamus to the cortex is well understood, but interactions between the cortex and higher-order (HO) nuclei, like the pulvinar, remain a mystery. Competing theories on the role of cortico-pulvino-cortical circuits remain unresolved. One model suggests that HO nuclei serve as relays for information transmission between cortical areas; while the alternative proposes a modulatory function promoted by reciprocal thalamocortical loops. Advances in viral tools for anatomical tracing and targeted perturbation of neuronal activity now allow us to test these hypotheses. This dissertation investigates the anatomical and functional relationship between the pulvinar and extrastriate cortex in the mouse in an attempt to understand the nature of higher-order thalamocortical interactions. In Chapter 1, we map the input/output relationships of distinct projection classes in the pulvinar. Using monosynaptic g-deleted rabies virus, we show that driving layer 5 cortical inputs to the pulvinar are organized as a feedforward, transthalamic relay. We also describe a broad network of modulatory layer 6 inputs which are biased towards reciprocal connections with the pulvinar. Bottom-up input from the superior colliculus (SC) targets every cortical pathway through the pulvinar. Chapter 2 investigates the functional contribution of a pulvinar → extrastriate pathway to visual activity in vivo in awake, passively viewing animals. We selectively target a single pulvinar projection population for optogenetic inactivation and compare the effects to inactivation of the FO pathway. Unlike FO thalamocortical input, which is necessary for sensory transmission, the HO input to cortex is not responsible for sensory responses. Instead, our results support a modulatory, excitatory contribution of the pulvinar to cortical activity. In summary, this study establishes a general framework for the anatomical organization of HO thalamocortical circuits, whereby the pulvinar provides a parallel path between cortical areas and a secondary route for bottom-up visual signals. Our physiological results highlight the folly in inferring circuit function from anatomy alone, however, as this transthalamic pathway does not drive visual activity under passive, head-fixed conditions. Instead, our findings describe a potential driving pathway between sensory cortices which might relay a non-sensory or context-dependent message. Additional functional studies that engage this circuit in active behavioral states will be necessary to solve the puzzle of the pulvinar.

The Visual Thalamocortical System and Its Modulation by the Brain Stem Core

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Release : 2012-12-06
Genre : Medical
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Book Rating : 011/5 ( reviews)

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Book Synopsis The Visual Thalamocortical System and Its Modulation by the Brain Stem Core by : Mircea Steriade

Download or read book The Visual Thalamocortical System and Its Modulation by the Brain Stem Core written by Mircea Steriade. This book was released on 2012-12-06. Available in PDF, EPUB and Kindle. Book excerpt: This monographic work authored by eminent neurophysiologists will be of major interest to researchers investigating the visual system or working in behavioral neuroscience and sleep research. The book deals with the neuronal circuits of the visual thalamocortical system, the brainstem and basal forebrain modulatory systems and their neurotransmitters acting upon these circuits, and the neuronal activities in the visual thalamocortical system as changed during shifts in behavioral states of vigilance from wake to sleep. Data discussed consist of recent studies on light and electron microscopy, extra- and intracellular recordings of thalamic and cortical neurons, neurotransmitter actions, and state-dependent cellular activities in the visual system.

The Cognitive Thalamus

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Release : 2015-06-17
Genre : Neurosciences. Biological psychiatry. Neuropsychiatry
Kind : eBook
Book Rating : 414/5 ( reviews)

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Book Synopsis The Cognitive Thalamus by : Yuri B. Saalmann

Download or read book The Cognitive Thalamus written by Yuri B. Saalmann. This book was released on 2015-06-17. Available in PDF, EPUB and Kindle. Book excerpt: Cognitive processing is commonly conceptualized as being restricted to the cerebral cortex. Accordingly, electrophysiology, neuroimaging and lesion studies involving human and animal subjects have almost exclusively focused on defining roles for cerebral cortical areas in cognition. Roles for the thalamus in cognition have been largely ignored despite the fact that the extensive connectivity between the thalamus and cerebral cortex gives rise to a closely coupled thalamo-cortical system. However, in recent years, growing interest in the thalamus as much more than a passive sensory structure, as well as methodological advances such as high-resolution functional magnetic resonance imaging of the thalamus and improved electrode targeting to subregions of thalamic nuclei using electrical stimulation and diffusion tensor imaging, have fostered research into thalamic contributions to cognition. Evidence suggests that behavioral context modulates processing in primary sensory, or first-order, thalamic nuclei (for example, the lateral geniculate and ventral posterior nuclei), allowing attentional filtering of incoming sensory information at an early stage of brain processing. Behavioral context appears to more strongly influence higher-order thalamic nuclei (for example, the pulvinar and mediodorsal nucleus), which receive major input from the cortex rather than the sensory periphery. Such higher-order thalamic nuclei have been shown to regulate information transmission in frontal and higher-order sensory cortex according to cognitive demands. This Research Topic aims to bring together neuroscientists who study different parts of the thalamus, particularly thalamic nuclei other than the primary sensory relays, and highlight the thalamic contributions to attention, memory, reward processing, decision-making, and language. By doing so, an emphasis is also placed on neural mechanisms common to many, if not all, of these cognitive operations, such as thalamo-cortical interactions and modulatory influences from sources in the brainstem and basal ganglia. The overall view that emerges is that the thalamus is a vital node in brain networks supporting cognition.

Higher-Order Processing in the Visual System

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Release : 2008-04-30
Genre : Psychology
Kind : eBook
Book Rating : 620/5 ( reviews)

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Book Synopsis Higher-Order Processing in the Visual System by : Gregory R. Bock

Download or read book Higher-Order Processing in the Visual System written by Gregory R. Bock. This book was released on 2008-04-30. Available in PDF, EPUB and Kindle. Book excerpt: Foremost neurophysiologists and psychophysicists provide pertinent information on the nature of representation at the earliest stages as this will constrain the disposition of all subsequent processing. This processing is discussed in several different types of visual perception.

Pathways and Cell Types Underlying Visual Perception in the Mouse

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Release : 2016
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Book Synopsis Pathways and Cell Types Underlying Visual Perception in the Mouse by : Ashley Juavinett

Download or read book Pathways and Cell Types Underlying Visual Perception in the Mouse written by Ashley Juavinett. This book was released on 2016. Available in PDF, EPUB and Kindle. Book excerpt: The primary challenge of systems neuroscience is identifying the circuits and cell types that underlie sensation and behavior. Faced with the daunting task of unraveling six layers of cortex, a hierarchy of visual areas, and a multitude of cell types, visual neuroscience relies on innovative technologies to achieve a circuit-level understanding of perceptual phenomena. This dissertation aims to be an extension of this effort by using advanced tools to address several longstanding questions regarding the structure and function of the visual system. In the past decade, mouse visual cortex has come to the forefront of systems neuroscience, serving as a common ground to study the role of cell types in behavior. Armed with a remarkable arsenal of genetic and molecular tools in transgenic mice, we are poised to observe and manipulate visual circuits in a cell-type specific manner. Yet doing so requires a comprehensive understanding of the system at hand. In the work presented here, I extend our knowledge of the mouse visual system so that we may exploit its experimental advantages to address circuit-level questions. Spanning multiple techniques and circuits, this dissertation investigates the mouse visual system from several angles. First, it refines our understanding of mouse visual cortex functional organization with bulk loaded calcium indicators and a well-studied higher-order stimulus, moving plaids (Chapter 1). Secondly, it characterizes the functional response properties of three different genetically defined layer 5 cell types, using in vivo two-photon imaging in the primary visual cortex (Chapter 2). Lastly, it delineates the topography of thalamocortical projections from the secondary visual thalamic nucleus (LP) to multiple visual cortical areas with classic tracing methods as well as novel viral combinations (Chapter 3). Together, these three studies advance our understanding of the connectivity and function of the mouse visual system, bringing us closer to bridging neurons and behavior.

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