Time/Room: Friday, May 11, 1:00 – 3:00 pm, Royal Ballroom 1-3
Organizer: Vivien A. Casagrande, PhD, Department of Cell & Developmental Biology, Vanderbilt Medical School Nashville, TN
Presenters: Gopathy Purushothaman, Christian Casanova, Heywood M. Petry, Robert H. Wurtz, Sabine Kastner, David Whitney
Symposium Description
The thalamus is considered the gateway to the cortex. Yet, even the late Ted Jones who wrote two huge volumes on the organization of the thalamus remarked that we know amazingly little about many of its components and their role in cortical function. This is despite the fact that a major two-way highway connects all areas of cortex with the thalamus. The pulvinar is the largest thalamic nucleus in mammals; it progressively enlarged during primate evolution, dwarfing the rest of the thalamus in humans. The pulvinar also remains the most mysterious of thalamic nucleus in terms of its function. This symposium brings together six speakers from quite different perspectives who, using tools from anatomy, neurochemistry, physiology, neuroimaging and behavior will highlight intriguing recent insights into the structure and function of the pulvinar. The speakers will jointly touch on: 1) the complexity of architecture, connections and neurochemistry of the pulvinar, 2) potential species similarities and differences in pulvinar’s role in transmitting visual information from subcortical visual areas to cortical areas, 3) the role of pulvinar in eye movements and in saccadic suppression, 4) the role of pulvinar in regulating cortico-cortical communication between visual cortical areas and finally, 5) converging ideas on the mechanisms that might explain the role of the pulvinar under the larger functional umbrella of visual salience and attention. Specifically, the speakers will address the following issues. Purushothaman and Casanova will outline contrasting roles for pulvinar in influencing visual signals in early visual cortex in primates and non- primates, respectively. Petry and Wurtz will describe the organization and the potential role of retino-tectal inputs to the pulvinar, and that of pulvinar projections to the middle temporal (MT/V5) visual area in primate and its equivalent in non-primates. Wurtz also will consider the role of pulvinar in saccadic suppression. Kastner will describe the role of the pulvinar in regulating information transfer between cortical areas in primates trained to perform an attention task. Whitney will examine the role of pulvinar in human visual attention and perceptual discrimination. This symposium should attract a wide audience from Visual Science Society (VSS) participants as the function of the thalamus is key to understanding cortical organization. Studies of the pulvinar and its role in vision have seen a new renaissance given the new technologies available to reveal its function. The goal of this session will be to provide the VSS audience with a new appreciation of the role of the thalamus in vision.
Presentations
Gating of the Primary Visual Cortex by Pulvinar for Controlling Bottom-Up Salience
Gopathy Purushothaman, PhD, Department of Cell & Developmental Biology Vanderbilt, Roan Marion, Keji Li and Vivien A. Casagrande Vanderbilt University
The thalamic nucleus pulvinar has been implicated in the control of visual attention. Its reciprocal connections with both frontal and sensory cortices can coordinate top-down and bottom-up processes for selective visual attention. However, pulvino-cortical neural interactions are little understood. We recently found that the lateral pulvinar (PL) powerfully controls stimulus-driven responses in the primary visual cortex (V1). Reversibly inactivating PL abolished visual responses in supra-granular layers of V1. Excitation of PL neurons responsive to one region of visual space increased 4-fold V1 responses to this region and decreased 3-fold V1 responses to the surrounding region. Glutamate agonist injection in LGN increased V1 activity 8-fold and induced an excitotoxic lesion of LGN; subsequently injecting the glutamate agonist into PL increased V1 activity 14-fold. Spontaneous activity in PL and V1 following visual stimulation were strongly coupled and selectively entrained at the stimulation frequency. These results suggest that PL-V1 interactions are well-suited to control bottom-up salience within a competitive cortico-pulvino-cortical network for selective attention.
Is The Pulvinar Driving or Modulating Responses in the Visual Cortex?
Christian Casanova, PhD, Univ. Montreal, CP 6128 Succ Centre-Ville, Sch Optometry, Montreal , Canada, Matthieu Vanni & Reza F. Abbas & Sébastien Thomas. Visual Neuroscience Laboratory, School of Optometry, Université de Montréal, Montreal, Canada
Signals from lower cortical areas are not only transferred directly to higher-order cortical areas via cortico-cortical connections but also indirectly through cortico-thalamo-cortical projections. One step toward the understanding of the role of transthalamic corticocortical pathways is to determine the nature of the signals transmitted between the cortex and the thalamus. Are they strictly modulatory, i.e. are they modifying the activity in relation to the stimulus context and the analysis being done in the projecting area, or are they used to establish basic functional characteristics of cortical cells? While the presence of drivers and modulators has been clearly demonstrated along the retino-geniculo-cortical pathway, it is not known whether such distinction can be made functionally in pathways involving the pulvinar. Since drivers and modulators can exhibit a different temporal pattern of response, we measured the spatiotemporal dynamics of voltage sensitive dyes activation in the visual cortex following pulvinar electrical stimulation in cats and tree shrews. Stimulation of pulvinar induced fast and local responses in extrastriate cortex. In contrast, the propagated waves in the primary visual cortex (V1) were weak in amplitude and diffuse. Co-stimulating pulvinar and LGN produced responses in V1 that were weaker than the sum of the responses evoked by the independent stimulation of both nuclei. These findings support the presence of drivers and modulators along pulvinar pathways and suggest that the pulvinar can exert a modulatory influence in cortical processing of LGN inputs in V1 while it mainly provides driver inputs to extrastriate areas, reflecting the different connectivity patterns.
What is the role of the pulvinar nucleus in visual motion processing?
Heywood M. Petry, Department of Psychological & Brain Sciences, University of Louisville, Martha E. Bickford, Department of Anatomical Sciences and Neurobiology, University of Louisville School of Medicine
To effectively interact with our environment, body movements must be coordinated with the perception of visual movement. We will present evidence that regions of the pulvinar nucleus that receive input from the superior colliculus (tectum) may be involved in this process. We have chosen the tree shrew (Tupaia belangeri, a prototype of early primates), as our animal model because tectopulvinar pathways are particularly enhanced in this species, and our psychophysical experiments have revealed that tree shrews are capable of accurately discriminating small differences in the speed and direction of moving visual displays. Using in vivo electrophysiological recording techniques to test receptive field properties, we found that pulvinar neurons are responsive to moving visual stimuli, and most are direction selective. Using anatomical techniques, we found that tectorecipient pulvinar neurons project to the striatum, amygdala, and temporal cortical areas homologous to the primate middle temporal area, MT/V5. Using in vitro recording techniques, immunohistochemistry and stereology, we found that tectorecipient pulvinar neurons express more calcium channels than other thalamic nuclei and thus display a higher propensity to fire with bursts of action potentials, potentially providing a mechanism to effectively coordinate the activity of cortical and subcortical pulvinar targets. Collectively, these results suggest that the pulvinar nucleus may relay visual movement signals from the superior colliculus to subcortical brain regions to guide body movements, and simultaneously to the temporal cortex to modify visual perception as we move though our environment.
One message the pulvinar sends to cortex
Robert H. Wurtz, NIH-NEI, Lab of Sensorimotor Research, Rebecca Berman, NIH-NEI, Lab of Sensorimotor Research
The pulvinar has long been recognized as a way station on a second visual pathway to the cerebral cortex. This identification has largely been based on the pulvinar’s connections, which are appropriate for providing visual information to multiple regions of visual cortex from subcortical areas. What is little known is what information pulvinar actually conveys especially in the intact functioning visual system. We have identified one pathway through the pulvinar that extends from superior colliculus superficial visual layers though inferior pulvinar (principally PIm) to cortical area MT by using the techniques of combined anti- and orthodromic stimulation. We now have explored what this pathway might convey to cortex and have first concentrated on a modulation of visual processing first seen in SC, the suppression of visual responses during saccades. We have been able to replicate the previous observations of the suppression in SC and in MT and now show that PIm neurons also are similarly suppressed. We have then inactivated SC and shown that the suppression in MT is reduced. While we do not know all of the signals conveyed through this pathway to cortex, we do have evidence for one: the suppression of vision during saccades. This signal is neither a visual nor a motor signal but conveys the action of an internal motor signal on visual processing. Furthermore combining our results in the behaving monkey with recent experiments in mouse brain slices (Phongphanphanee et al. 2011) provides a complete circuit from brainstem to cortex for conveying this suppression.
Role of the pulvinar in regulating information transmission between cortical areas
Sabine Kastner, MD, Department of Psychology, Center for Study of Brain, Mind and Behavior, Green Hall, Princeton, Yuri B. Saalman, Princeton Neuroscience Institute, Princeton University
Recent studies suggest that the degree of neural synchrony between cortical areas can modulate their information transfer according to attentional needs. However, it is not clear how two cortical areas synchronize their activities. Directly connected cortical areas are generally also indirectly connected via the thalamic nucleus, the pulvinar. We hypothesized that the pulvinar helps synchronize activity between cortical areas, and tested this by simultaneously recording from the pulvinar, V4, TEO and LIP of macaque monkeys performing a spatial attention task. Electrodes targeted interconnected sites between these areas, as determined by probabilistic tractography on diffusion tensor imaging data. Spatial attention increased synchrony between the cortical areas in the beta frequency range, in line with increased causal influence of the pulvinar on the cortex at the same frequencies. These results suggest that the pulvinar co-ordinates activity between cortical areas, to increase the efficacy of cortico-cortical transmission.
Visual Attention Gates Spatial Coding in the Human Pulvinar
David Whitney, The University of California, Berkeley, Jason Fischer, The University of California, Berkeley
Based on the pulvinar’s widespread connectivity with the visual cortex, as well as with putative attentional source regions in the frontal and parietal lobes, the pulvinar is suspected to play an important role in visual attention. However, there remain many hypotheses on the pulvinar’s specific function. One hypothesis is that the pulvinar may play a role in filtering distracting stimuli when they are actively ignored. Because it remains unclear whether this is the case, how this might happen, or what the fate of the ignored objects is, we sought to characterize the spatial representation of visual information in the human pulvinar for equally salient attended and ignored objects that were presented simultaneously. In an fMRI experiment, we measured the spatial precision with which attended and ignored stimuli were encoded in the pulvinar, and we found that attention completely gated position information: attended objects were encoded with high spatial precision, but there was no measurable spatial encoding of actively ignored objects. This is despite the fact that the attended and ignored objects were identical and present simultaneously, and both attended and ignored objects were represented with great precision throughout the visual cortex. These data support a role for the pulvinar in distractor filtering and reveal a possible mechanism: by modulating the spatial precision of stimulus encoding, signals from competing stimuli can be suppressed in order to isolate behaviorally relevant objects.