International Conference on Parietal Lobe Function
Artis Zoo, Amsterdam | 20-21 September 2010
Abstracts
Mick Rugg
Masud Husain
Jon Kaas
Claudio Galletti and Patrizia Fattori
Alexandra Battaglia-Mayer
Matthew FS Rushworth, Erie D Boorman, Rogier B Mars
Stephen Jackson
Ivan Toni
Laurel Buxbaum
Jody Culham
Chris Dijkerman
Salvador Soto Faraco
Ellen Poliakoff
Brigitte Röder
Brian Butterworth
Martin Fischer
Rainer Goebel
Mick Rugg
What is the role of lateral parietal cortex in episodic memory retrieval?
Since the earliest functional neuroimaging studies of human memory it has been apparent that the lateral parietal cortex is consistently activated during retrieval of episodic memories. Given the paucity of neuropsychological evidence pointing to a role for this region in memory these findings are unexpected, and their interpretation remains controversial. This presentation will review evidence indicating that memory retrieval activates at least two functionally dissociable regions of the lateral parietal cortex: the middle segment of the intra-parietal sulcus (IPS) and the posterior aspect of the angular gyrus. The relative merits of two approaches to the interpretation of these findings – one based on the role of the lateral parietal cortex in attention, and the other proposing a more direct involvement in memory – will be discussed in light of the experimental evidence. Recent findings concerning the consequences for memory function of lateral parietal damage, and the use of functional connectivity analyses to segregate lateral parietal cortex, will also be discussed.
Masud Husain
Attention, working memory and parietal cortex
One important way to examine the contribution of parietal cortex to cognitive functions is by observing the deficits that follow lesions to this region. In humans, damage to the parietal lobe, particularly in the right hemisphere, leads to the syndrome of neglect or inattention to objects in contralesional space. Recent studies have begun to dissect the interacting, cognitive mechanisms that might underlie neglect, providing important insights into the role of posterior parietal cortex (PPC) in directing spatial attention, maintaining vigilance or sustained attention and in visual working memory. For example, although the deployment of spatial attention is known to be impaired in neglect there has been relatively little investigation of whether the deficit is stimulus-driven or goal-directed. We probed the nature of the attention deficit using eye movements to measure bottom-up capture by irrelevant stimuli while patients were performing a goal-directed search. Our findings reveal similar, graded deficits across space for both stimulus-driven and goal-directed attention, consistent with the view that PPC makes a crucial contribution to both these processes. Separate experiments also reveal that neglect patients have difficulty maintaining attention to spatial locations over time. A vigilance decrement was observed in such individuals when they were required to maintain attention to spatial locations, but not verbal or pattern material. Finally, recent findings have 6 begun to show impairments in the precision of visual working memory – for object orientation as well as for spatial locations – in neglect, even when stimuli are presented centrally at fixation. In this talk, I’ll review these findings and consider what they might reveal about the contributions of the human right PPC to attention and working memory.
Jon Kaas
The evolution of dorsal stream somatosensory networks in primates.
Comparative studies of cortical organization in mammals allow the evolution of the complex organization of parietal cortex in humans to be reconstructed. Early mammals had small brains with little neocortex. They likely had a primary somatosensory area, S1, adjoining rostral and caudal somatosensory belts, and one (S2) or more (S2 and PV) higher-order somatosensory areas, but little that could be called posterior parietal cortex (PPC), and no motor cortex, and a narrow region of PPC emerged with placental mammals, providing substrates for a dorsal stream sensorimotor network that included both somatosensory and visual inputs. The immediate ancestors of primates had an expanded region of visual cortex, and possibly more visual input into the still small PPC. By comparison, PPC is greatly expanded in all extant primates. Early primates likely resembled present-day prosimians i having little change in the organization of anterior parietal cortex, while having much more PPC, which was divided into a rostral half dominated by somatosensory inputs and a caudal half dominated by visual inputs, which were then relayed to the rostral half. In present-day prosimian galagos, rostral PPC contains crude representations of body movements from limbs to forelimb and hand, to face in a mediolateral sequence, as revealed by electrical stimulation with microelectrodes. Subregions can be defined that produce reaching, grasping, and defensive movements, and similar movement regions exist in motor and premotor cortex. These frontal and parietal subregions are preferentially interconnected. Similar subregions have been demonstrated in New World monkeys, and in motor and premotor cortex of Old World monkeys, and they likely exist in all primates. Yet, the somatosensory cortex of anthropoid primates has changed from that of prosimian-like ancestors in a number of ways, including a more differentiated anterior parietal region with a complex body representation in Area 2, expanded lateral parietal cortex with additional areas, and a variably larger PPC with additional subdivisions, especially in humans. Overall, the expanded and functionally subdivided PPC of anthropoid primates is thought to mediate the intentions for specific motor behaviors, as well as use sensory information to guide performance. We propose that interconnections between functional subdivisions of PPC allow a single behavior to emerge in response to sensory stimuli while inhibiting others.
Claudio Galletti and Patrizia Fattori
Reaching and grasping activities in the medial posterior parietal cortex of the primate brain
Recording from single neurons in the macaque brain in the last decades has provided an useful tool to get insights on how the brain organises complex processes. The dorsal visual stream, involving superior and inferior parietal lobules, is strongly involved in object location and in control of reach-to-grasp actions (Goodale and Milner, 1992). The superior parietal lobule in particular is though to be involved in the on-line processing of visual information for the purpose of directing the hand towards objects to be reached and grasped. Area V6A is a visuomotor area of the caudalmost part of the superior parietal lobule that shows interesting functional properties to this respect. Single V6A cells are modulated by visual and oculomotor signals, as well as by somatic signals from the upper limbs and by arm-reaching movements. V6A neurons use a complex frame of reference that encompasses both spatial and retinotopic coordinates. V6A cells are likely involved in the neural computations needed to guide the entire act of prehension, from the transport of the hand towards the object in the peripersonal space, to the hand orientation and preshaping to align it and shape it correctly to acquire the object. According to these findings, reaching and grasping would be processed by the same population of posterior parietal neurons. This could shed new light on the way the brain plans and executes visually guided action.
Grants: FP7-ICT 217077-EYESHOTS , MIUR, Fondazione del Monte di Bologna e Ravenna
Alexandra Battaglia-Mayer
The role of parietal cortex in the on-line control of hand Movement: a comparison with frontal cortex.
An important aspect of the control of hand movement is the capability to quickly update the hand trajectory, whenever requested by the external environment, such as when an unexpected change of target location occurs during planning and execution of hand movement. There is evidence that this ability is affected after disruption of parietal neural mechanisms, e.g. as a consequence of cortical lesions or of transient cortical inactivation. To understand the role of the posterior parietal cortex (PPC) within the parieto-frontal network, we have recorded neural activity in PPC (area 5), as well as in dorsal premotor cortex (PMd) of macaque monkeys, trained to make reaches to visual targets in 3D space and on-line corrections of movement trajectory, after sudden change of target location in space. It was found that both parietal and premotor activity are highly correlated with the changes in hand kinematics, although this correlation remains higher for parietal than for premotor cortex during trajectory correction. However, another differential roles of these areas emerge when looking at the timing of their activation, in particular the time of signalling the change of motor intention. In such a case, PMd activity leads parietal activity, 8 suggesting that the former is mainly involved in encoding the higher-order instruction to initiate a new motor plan, while the latter is more involved in the current state estimation of motor periphery during planning an initial hand movement and updating his trajectory.
Matthew FS Rushworth, Erie D Boorman, Rogier B Mars
Parietal-frontal interactions in people and macaques
The similarity between the parietal cortex in the human brain and in the brains of other primates has been questioned. There has been a particular focus on the possibility that the human inferior parietal lobule (IPL) might differ from the IPL in other primate species. To better characterize the human parietal cortex we used diffusion weighted magnetic resonance imaging (DW-MRI) and probabilistic tractography to estimate connectivity profiles between each voxel in the human parietal cortex and the rest of the brain and then used similarities in the patterns of connexions to parcellate the parietal cortex into component regions. Ten regions were consistently identified in all subjects using this approach and most of the areas corresponded to cytoarchitectonically defined parietal regions. Patterns of correlation between the resting state BOLD signal in the parietal areas and areas known to be interconnected with the parietal cortex in the macaque were then examined in both humans and macaques. The resulting resting state “functional connectivity” patterns in the macaque reflected the known structural connexions of the parietal cortex. Moreover, there were clear similarities between the functional connectivity patterns associated with both human and macaque parietal cortex that suggested fundamental similarities between parietal cortical organization in the two species. It was notable, however, that activity in the human mid-IPL was strongly correlated with activity in a very anterior prefrontal brain region and a similar pattern was not easily discerned in the macaque. A functional magnetic resonance imaging (fMRI) study suggested that activity in the two areas reflected evidence in favour of an alternative course of action that might be taken each time a subject made a choice. Functional connectivity between the two areas was enhanced as the subjects switched to alternative courses of action.
Stephen Jackson
Parietal contributions to the planning and control of reaching movements
Computational theories have proposed that the brain uses internal models of the body to ensure accurate control of movement. Specifically, forward ‘dynamic’ models are thought to generate an estimate of the next motor state for an upcoming movement: thereby providing a dynamic representation of the current 9 postural configuration of the body that can be utilised during movement planning and execution. It has been suggested that a representation of the current state estimate of the arm is maintained in the superior lobule of the posterior parietal cortex [SPL] and consistent with this view, damage to the SPL often leads to an impairment of reaching movements. In this paper I review recent neuropsychological, transcranial magnetic stimulation, and fMRI studies that have investigated the contributions of the SPL to the planning and control of reaching movements.
Ivan Toni
How many brain areas does it take to grasp a light bulb?
Until recently, our understanding of reaching-to-grasp behavior was one of the success stories of neuroscience, with a detailed characterization of the control variables, neuronal structures, and cerebral circuits supporting it. In short, visuospatial information about the spatial location of a grasped object relative to the subject would be processed along a dorso-medial parieto-frontal circuit, whereas visuospatial information about the size, shape, and orientation would be processed along a dorso-lateral parieto-frontal circuit. However, the lack of an expected event has started to cast doubts on this success story. Despite the supposedly anatomical and functional segregation between these two parieto- frontal circuits, no clear double dissociation between reaching and grasping deficits following localized lesions has been found, to date. Furthermore, in the traditional model of reaching-to-grasp, it remains unclear how reaching and grasping components could be seamlessly coordinated and integrated with perceptual information. In this talk, I will use recent neurophysiological findings on reaching-to-grasp behavior to suggest a revision of that traditional model, and more generally to provide an example of how the primate brain integrates perceptual and motor processes.
Laurel Buxbaum
Form and Function: Interactions and conflicts between actions associated with objects
A number of lines of evidence suggest that the parietal cortex is the locus of two distinct types of object-related action systems. The first is a bilateral system calculating movements of the arm and hand based on currently-visualized structural information about object shape, size, and location. The second is a left- lateralized system richly informed by object semantics, which retrieves representations of skilled actions in the service of functional goals. These two systems, while strongly interactive, display different characteristics in terms of temporal persistence of activated information, and thus have different 10 propensities to participate in between- and within-object priming and interference. Moreover, they are differentially damaged in patients with action disorders (apraxias), resulting in difficulties with resolution of response conflict that lead to action errors. Review of these findings and directions for future research will be discussed.
Jody Culham
Parietal coding of movement components and object properties in reaching and grasping
Functional magnetic resonance imaging of human parietal cortex has identified two key areas involved in reach and reach-to-grasp movements. The anterior intraparietal sulcus (aIPS) codes the hand grip and is affected by object properties such as size. The superior parieto-occipital cortex (SPOC) codes the transport of the arm and orientation of the wrist. Recent multivoxel pattern analysis results show that information from aIPS and SPOC can be used to decode grasping vs. reaching movements during movement planning as well as action execution. Information from other parietal and frontal areas can be used to decode precision grips on large vs. small objects. Taken together, these results suggest although information about movement components (arm, hand, wrist) and the target object (size, location) must ultimately be integrated to produce seamless reach-to-grasp actions, various subregions of parietal and frontal cortex may code different types of information.
Chris Dijkerman
Somatosensory representations of the fingers. Evidence from finger agnosia and spatial directional judgements
Several authors have proposed that fingers are represented differently to other body parts. Evidence for this notion comes from neuropsychological studies of patients with finger agnosia as well as from psychophysical studies. In this talk I will focus on how tactile input from different fingers is processed in healthy individuals and in patients with finger agnosia. First, finger agnosia affects identification of the touched finger, but not goal-directed movements towards that finger. In a second study we observed that finger agnosia does not affect the ability to integrate tactile input from different fingers into a coherent percept or to make spatial judgements about them. Finally, a study of spatial directional judgements with healthy individuals reveals somatotopic mapping of tactile input when the fingers have been crossed. Together, these findings suggest different levels of processing tactile input from the fingers. Finger agnosia is an impairment of finger identification, however the ability to distinguish between tactile input from different fingers is not impaired at all levels. Indeed spatial judgements about tactile stimuli are spared, which may depend particularly on somatotopic representations.
Salvador Soto Faraco
The remapping of tactile space
Reacting to sensation on the skin, like when we swat a mosquito from our forearm, requires a spatial transformation from a skin-centered spatial representation to an external reference frame. I will present data from several studies addressing the nature of the representations involved in this process of spatial remapping, its time course and its potential neural underpinnings. First, we have found that two different spatial frames of reference are available at different times during the encoding of touch. In particular, a fleeting representation linked to anatomically-based space is quickly followed by a more stable, abstract representation based on an external spatial frame of reference. This reference-frame transformation turns out to be relatively automatic and independent of the spatial requirements of the task. Second, we have investigated the time course of tactile remapping by means of somatosensory evoked potentials (SEPs) and saccadic responses. In both cases, we compared participants’ reactions to a single tactile event at one hand under crossed- and uncrossed-hands posture. SEPs revealed effects of posture on somatosensory processing as early as ~80 ms post stimulus, thus suggesting an onset time of remapping. Saccadic RTs and trajectories, on the other hand, confirmed that an external representation about touch location is already available ~270 ms after stimulus presentation. Finally, we used transcranial magnetic stimulation (TMS) to investigate the involvement of the human homologue of ventral intra parietal (hVIP) area in tactile remapping. Participants compared the elevation of arm taps with respect to face taps across different postures, a task that requires the use of an external representation of tactile location. Our results revealed that single-pulse TMS targeted at the right hVIP disrupted performance in this task, but not in other tasks which could be resolved on the basis of purely somatosensory or proprioceptive information. Therefore, hVIP seems to play a causal role in high-level spatial transformations leading tactile information from a primary, anatomically based representation, to a more abstract externally based coordinate system.
Ellen Poliakoff
Investigating Somatic Perception and Misperception
When detecting the presence or absence of weak tactile targets, people frequently miss targets and falsely report a tactile sensation in the absence of a stimulus (false alarms). In the somatic signal detection task (SSDT), we have observed that tactile false alarms increase in the presence of a concurrent light (Lloyd et al., 2008). I will present results from two recent studies in which we have recorded brain activity using functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) whilst participants performed the SSDT task. Specifically, we have examined how brain activity differs when participants i) correctly report versus miss a weak touch; ii) falsely report versus correctly reject an absent touch. We predicted that we would observe activity in 12 somatosensory and parietal areas and the medial prefrontal cortex, which has been linked to subjective reports of vibration detection in non-human primates (de Lafuente & Romo, 2005). Results will be discussed in terms of the similarities and differences between tactile experience in the presence and absence of a stimulus.
Brigitte Röder
Crossmodally generated shifts of auditory localization
When an auditory and a visual event are presented from two different locations, people often report to hear the sound close to the location of the visual stimulus, a phenomenon well known as the ventriloquist effect. As we showed, a similar ventriloquist effect exists for audio-tactile stimuli. By systematically varying the hand posture (uncrossed vs. crossed) we were able to conclude that tactile stimuli modulate auditory localization base on external rather than anatomical coordinates. An event-related potential study further suggested that the audio- tactile ventriloquist effect, similar as has been reported for the audio-visual ventriloquist effect, is predominantly mediated by feedback connections from multisensory cortex to auditory cortex. A repeated presentation of spatially discrepant audio-visual stimuli results in a shift of auditory localization, a phenomenon known as the ventriloquist aftereffect, which can last for tens of minutes after the visual stimuli were removed. Using event-related potentials we tested whether the ventriloquist aftereffect results from a prevailing activity of feedback connections from multisensory regions to auditory cortex or whether a change of auditory spatial representations involved in bottom up processing mediate the ventriloquist after effect. We interpreted the finding that the N1 amplitude to sounds was altered by a preceding repetitive ventriloquist experience as evidence for the second hypothesis. Taken together these findings might reflect a general principle of crossmodal adaptations in adulthood: Crossmodal learning experience modulates sensory cortex via feedback connections. These changes prevail and result in a change of unisensory perception.
Brian Butterworth
Numbers and space in the parietal lobes and elsewhere
Although it is well-established that the parietal lobes are a core locus for numerical processing, there are two important unanswered questions. First, do both left and right parietal lobes do the same job? There is now evidence that lateralization of function changes in the course of development, and that the left hemisphere is more engaged in calculation while the right more in estimation. There also appear to be regional differences of function within each lobe, with 13 left angular gyrus being involved arithmetical fact retrieval (no surprise there) and the right temporo-parietal junction supporting subitizing. Second, are spatial models of numerical magnitude part of that job? Evidence from lesion studies and TMS suggest that both right inferior frontal gyrus and frontal eye fields are contributors to the task-specific creation of a spatial model of numbers.
Martin Fischer
From sensory-motor associations to embodied numerical cognition
Numbers are no longer thought of as abstract and amodal concepts that we manipulate to compute quantities. Instead, number concepts have specific sensory and motor associations. I will review recent support for such sensory and motor biases in numerical cognition, focusing largely on behavioural evidence. To account for these findings I propose a theoretical framework for an embodied representation of number magnitude, according to which numerical concepts are grounded, embodied and situate
Rainer Goebel
Disentangling the functional role of the left and right parietal lobe in spatial mental tasks using fMRI and TMS
The capacity to generate and analyze mental visual images is essential for many cognitive abilities. A series of fMRI and TMS studies will be presented that support the notion that the left parietal lobe is predominant in generating mental images, whereas the right parietal lobe is specialized in the spatial comparison of the imagined content. Furthermore, our TMS studies indicate that the right, but not left, parietal cortex is able to immediately compensate a left parietal disruption by taking over the specific function of the left hemisphere. We found a similar hemispheric specialization for visuaspatial judgement tasks, i.e. impairments in task performance were only observed when stimulating the right parietal lobule. Finally network analyses revealed significant correlations between induced behavioral impairment and neural activity changes in both the directly stimulated parietal as well as remote ipsilateral frontal brain regions. This corroborates the notion that visuospatial deficits following parietal damage are brought about by a perturbation of activity across a specific frontoparietal network, rather than the lesioned parietal site alone. Our experiments furthermore show how sequential and concurrent fMRI and magnetic brain stimulation during active task execution hold the potential to identify and visualize networks of brain areas that are functionally related to specific cognitive processes.
