Time/Room: Friday, May 13, 2016, 5:00 – 7:00 pm, Pavilion
Organizer(s): Yaoda Xu and David Freedman; Harvard University and University of Chicago
Presenters: Sabine Kastner, Yaoda Xu, Jacqueline Gottlieb, David Freedman, Peter Janssen, Melvyn Goodale
Symposium Description
The primate parietal cortex has been associated with a diverse set of operations. Early evidence has highlighted the role of this brain region in spatial, attention, and action related processing. More recent evidence, however, has suggests a role for parietal cortex in non-spatial and cognitive functions such as object representation, categorization, short-term memory, number processing and decision making. How should we understand its function, given the wide array of sensory, cognitive and motor signals found to be encoded in parietal areas? Are there functionally dissociable regions within the primate parietal cortex, each participating in distinct functions? Or are the same parietal regions involved in multiple functions? Is it possible to form a unified account of parietal cortex’s role in perception, action and cognition? In this symposium, by bringing together researchers from monkey neurophysiology and human brain imaging, we will first ask the speakers to present our current understanding regarding the role of parietal cortex in visual spatial, non-spatial and cognitive functions. We will then ask the speakers whether the framework they have developed to understand parietal involvement in a particular task setting can help understand its role in other task contexts and whether there are fundamental features of parietal cortex that enable it to participate in a diverse set of tasks and functions. There will be a total of six speakers. Sabine Kastner will address spatial mapping, attention priority signals and object representations in human parietal cortex. Yaoda Xu will describe human parietal cortex’s involvement in visual short-term memory and object representation and their correspondence with behavior. Jacqueline Gottlieb will describe attention and decision related signals in monkey parietal cortex. David Freedman will examine monkey parietal cortex’s involvement in visual categorization, category learning, and working memory and its interaction with other cortical areas. Peter Janssen will detail the functional organization of the monkey intraparietal sulcus in relation to grasping and 3D object representation. Melvyn Goodale will discuss the role of the parietal cortex in the control of action.
Presentations
Comparative studies of posterior parietal cortex in human and non-human primates
Speaker: Sabine Kastner; Department of Psychology and The Princeton Neuroscience Institute, Princeton University
The primate parietal cortex serves many functions, ranging from integrating sensory signals and deriving motor plans to playing a critical role in cognitive functions related to object categorization, attentional selection, working memory or decision making. This brain region undergoes significant changes during evolution and can therefore serve as a model for a better understanding of the evolution of cognition. I will present comparative studies obtained in human and non-human primates using basically identical methods and tasks related to topographic and functional organization, neural representation of object information and attention-related signals. Topographic and functional mapping studies identified not only the parietal regions that primate species have in common, but also revealed several human-specific areas along the intraparietal sulcus. FMRI studies on parietal object representations show that in humans, they resemble those typically found in ventral visual cortex and appear to be more complex than those observed in non-human primates suggesting advanced functionality possibly related to the evolving human-specific tool network. Finally, electrophysiological signatures of parietal attention signals in space-based attention tasks are similar in many respects across primate species providing evidence for preserved functionality in this particular cognitive domain. Together, our comparative studies contribute to a more profound understanding of the evolution of cognitive domains related to object perception and attention in primates.
Decoding Visual Representations in the Human Parietal Cortex
Speaker: Yaoda Xu; Psychology Department, Harvard University
Although visual processing has been mainly associated with the primate occipital/temporal cortices, the processing of sophisticated visual information in the primate parietal cortex has also been reported by a number of studies. In this talk, I will examine the range of visual stimuli that can be represented in the human parietal cortex and the nature of these representations in terms of their distractor resistance, task dependency and behavioral relevance. I will then directly compare object representation similarity between occipital/temporal and parietal cortices. Together, these results argue against a “content-poor” view of parietal cortex’s role in attention. Instead, they suggest that parietal cortex is “content-rich” and capable of directly participating in goal-driven visual information representation in the brain. This view has the potential to help us understand the role of parietal cortex in other tasks such as decision-making and action, both of which demand the online processing of visual information. Perhaps one way to understand the function of parietal cortex is to view it as a global workspace where sensory information is retained, integrated, and evaluated to guide the execution of appropriate actions.
Multi-dimensional parietal signals for coordinating attention and decision making
Speaker: Jacqueline Gottlieb; Department of Neuroscience, Kavli Institute for Brain Science, Columbia University
In humans and non-human primates, the parietal lobe plays a key role in spatial attention – the ability to extract information from regions of space. This role is thought to be mediated by “priority” maps that highlight attention-worthy locations, and provide top-down feedback for motor orienting and attention allocation. Traditionally, priority signals have been characterized as being purely spatial – i.e., encoding the desired locus of gaze or attention regardless of the context in which the brain generates that selection. Here I argue, however, based on non-spatial modulations found in the monkey lateral intraparietal area, that non-spatial responses are critical for allowing the brain to coordinate attention with action – i.e., to estimate the significance and relative utility of competing sensory cues in the immediate task context. The results prompt an integrative view whereby attention is not a disembodied entity that acts on sensory or motor representations, but an organically emerging process that depends on dynamic interactions within sensorimotor loops.
Categorical Decision Making and Category Learning in Parietal and Prefrontal Cortices
Speaker: David Freedman; Department of Neurobiology and Grossman Institute for Neuroscience, Quantitative Biology, and Human Behavior, The University of Chicago
We have a remarkable ability to recognize the behavioral significance, or category membership of incoming sensory stimuli. In the visual system, much is known about how simple visual features (such as color, orientation and direction of motion) are processed in early stages of the visual system. However, much less is known about how the brain learns and recognizes categorical information that gives meaning to incoming stimuli. This talk will discuss neurophysiological and behavioral experiments aimed at understanding the mechanisms underlying visual categorization and decision making, with a focus on the impact of category learning on underlying neuronal representations in the posterior parietal cortex (PPC) and prefrontal cortex (PFC). We recorded from PPC both before and after training on a visual categorization task. This revealed that categorization training influenced both visual and cognitive encoding in PPC, with a marked enhancement of memory-related delay-period encoding during the categorization task which was not observed during a motion discrimination task prior to categorization training. In contrast, the PFC exhibited strong delay-period encoding during both discrimination and categorization tasks. This reveals a dissociation between PFC’s and PPC’s roles in decision making and short term memory, with generalized engagement of PFC across a wider range of tasks, in contrast with more task-specific and training dependent mnemonic encoding in PPC.
The functional organization of the intraparietal sulcus in the macaque monkey
Speaker: Peter Janssen; Laboratory for Neuro- and Psychophysiology, Department of Neurosciences, KU Leuven
The lateral bank of the anterior intraparietal sulcus (IPS) is critical for object grasping. Functional magnetic resonance imaging (fMRI) (Durand et al., 2007) and single-cell recording studies (Srivastava, Orban, De Maziere, & Janssen, 2009) in macaque monkeys have demonstrated that neurons in the anterior intraparietal area (AIP) are selective for disparity-defined three-dimensional (3D) object shape. Importantly, the use of the same stimuli and tasks in macaque monkeys and humans has enabled us to infer possible homologies between the two species. I will review more recent studies combining fMRI, single-cell recordings, electrical microstimulation and reversible inactivation that have shed light on the functional organization of the IPS. Using an integrated approach (Premereur, Van Dromme, Romero, Vanduffel, & Janssen, 2015), we could identify differences in the effective connectivity between nearby patches of neurons with very similar response properties, resolving a long-standing controversy between anatomical and physiological studies with respect to the spatial extent of neighboring areas AIP and LIP. In addition, the effective connectivity of the different IPS sectors has clarified the functional organization of the anterior IPS. Finally, reversible inactivation during fMRI can demonstrate how visual information flows within the widespread functional network involved in 3D object processing. These results are not only critical to understand the role of the macaque parietal cortex, but will also contribute to a better understanding of the parietal cortex in humans.
The role of the posterior parietal cortex in the control of action
Speaker: Melvyn Goodale; The Brain and Mind Institute, The University of Western Ontario
A long history of neuropsychological research has shown the visual control of grasping and other skilled movements depends on the integrity of visual projections to the dorsal visual stream in the posterior parietal cortex. Patients with lesions to the dorsal stream are unable to direct their hands towards or grasp visual targets in the contralesional visual field, despite being able to describe the size, orientation, and location of those targets. Other patients with lesions to the ventral stream are able to grasp objects accurately and efficiently despite being unable to report the very object features controlling their actions. More recent imaging studies of both neurological patients and healthy controls has confirmed the role of the dorsal stream in transforming visual information into the required coordinates for action. In this presentation, I will discuss research from our lab showing that visual information about the metrical properties of goal objects may reach the dorsal stream via pathways that bypass the geniculostriate pathway. I will go on to show that manual interactions with some classes of objects, such as tools, requires that visual information about those objects be processed by circuits in both the ventral and the dorsal stream. Finally, I will speculate that some of the other higher-order functions of the parietal lobe, such as its evident role in numerical processing and working memory, may have evolved from the need to plan actions to multiple goals.