The posterior parietal cortex and long-term memory representation of spatial information

The hypothesis to be explored in this chapter is based on the assumption that the posterior parietal cortex (PPC) is directly involved in representing a subset of the spatial features associated with spatial information processing and plays an important role in perceptual memory as well as long-term memory encoding, consolidation, and retrieval of spatial information. After presentation of the anatomical location of the PPC in rats, the nature of PPC representation based on single spatial features, binding of visual features associated with visual spatial attention, binding of object-place associations associated with acquisition and storage of associations where one of the elements is a spatial component, and binding of ideothetic and allothetic information in long-term memory is discussed. Additional evidence for a PPC role in mediation of spatial information in long-term storage is offered. Finally, the relationship between the PPC and the hippocampus from a systems and dynamic point view is presented.     

Role of the parietal cortex in long-term representation of spatial information in the rat

The processing of spatial information in the brain requires a network of structures within which the hippocampus plays a prominent role by elaborating an allocentric representation of space. The parietal cortex has long been suggested to have a complementary function. An overview of lesion and unit recording data in the rat indicates that the parietal cortex is involved in different aspects of spatial information processing including allocentric and egocentric processing. More specifically, the data suggest that the parietal cortex plays a fundamental role in combining visual and motion information, a process that would be important for an egocentric-to-allocentric transformation process. Furthermore, the parietal cortex may also have a role in the long-term storage of representation although this possibility needs further evidence. The data overall show that the parietal cortex occupies a unique position in the brain at the interface of perception and representation.     

Posterior parietal cortex as part of a neural network for directed attention in rats

A rodent model of directed attention has been developed based upon behavioral analysis of contralateral neglect, pharmacological manipulations, and anatomical analysis of neural circuitry. In each of these three domains the rodent model exhibits striking similarities to humans. We hypothesize that there is a specific thalamo-cortical-basal ganglia network that subserves spatial attentional functions. Key components of this network are medial agranular and posterior parietal cortex, dorsocentral striatum, and the lateral posterior thalamic nucleus. Several issues need to be addressed before we can hope to realistically understand or model the functions of this network. Among these are the roles of medial versus lateral posterior parietal cortex; cholinergic mechanisms in attention; interhemispheric interactions; the role of synchronous firing at the cortical, striatal, and thalamic levels; interactions between cortical and thalamic projections to the striatum; interactions between cortical and nigral inputs to the thalamus; the role of collicular inputs to the lateral posterior thalamic nucleus; the role of cerebral cortex versus superior colliculus in driving the motor output expressed as orienting behavior during directed attention; the extent to which the circuitry we describe for directed attention also plays a role in other forms of attention.     

Different time course for the memory facilitating effect of bicuculline in hippocampus, entorhinal cortex, and posterior parietal cortex of rats

Several lines of evidence indicate that gamma-aminobutyric acid (GABA) type A (GABA(A)) receptors regulate memory consolidation. Here we studied the effect on consolidation of the selective antagonist of GABA(A) receptors, bicuculline, given into several regions of the cortex at different times after one-trial step-down inhibitory avoidance (0.5 mA, 2-s footshock). Rats were bilaterally implanted with cannulae aimed at the CA1 region of the dorsal hippocampus, entorhinal cortex or posterior parietal cortex, three areas known to be involved in the memory consolidation of this task. At different times after training, bicuculline (0.5 microg/side) was infused into the above mentioned structures. Bicuculline increased memory retention when administered either immediately or 1.5h after training into CA1, and both immediately and 3h after training in the entorhinal or parietal cortex. Thus, in agreement with previous findings using other drugs, the response was biphasic in these latter structures. This suggests that GABAergic mechanisms normally downregulate, memory processing by inhibiting on-going activities necessary for consolidation at the times in which bicuculline was effective in each structure. Based on previous findings, in the hippocampus, such activity involves a number of receptors and signaling pathways in the first 1.5h after training. In the entorhinal and parietal cortex memory-related activities include the participation of protein kinase A and extracellularly regulated kinase (ERK) twice, right after training and then again 3h later.     

Retrosplenial cortex lesion affected segregation of spatial information in place avoidance task in the rat

Retrosplenial cortex (RSC) together with the hippocampus is a component of the spatial memory circuit. To elucidate the role of the RSC in spatial memory formation in the immediate presence of both relevant and irrelevant spatial stimuli, we used a new place avoidance task, in which rats learn to avoid shock in an unmarked place. In the present study, we manipulated the relevance of distal "Room" stimuli and local "Arena" stimuli for place avoidance. Rats with ibotenate lesions of RSC, control sham lesions (Csl) and intact control rats (Cint) initially learned the (Room&Arena)+ task variant in which both Room and Arena stimuli are relevant for defining the shock sector. Afterwards, different subsets of rats from each group were trained in the following task variants: (i) Room+Arena-, in which the arena continuously rotated so that Room stimuli were relevant and Arena stimuli were irrelevant for avoiding shock; (ii) Arena+, in which the arena and shock sector rotated in a dark room so that Arena stimuli were relevant and Room stimuli were irrelevant for avoiding shock; (iii) Room+, in which the arena was covered in shallow water so that only Room stimuli were relevant for avoiding the shock sector whether the arena was stationary or rotating. We found that damage of RSC impaired the Room+Arena- variant that required relevant and irrelevant stimuli to be segregated. Importantly, the same lesions spared task variants that did not require segregation. Our results suggest an involvement of retrosplenial cortex in the segregation of spatial information.     

At your own peril: An ERP study of voluntary task set selection processes in the medial frontal cortex

A tool that is commonly used to investigate selection among different alternatives in a changing environment is the task-switching paradigm. Functional neuroimaging has pointed out a role for the posterior medial frontal cortex and the posterior parietal cortex in the voluntary selection of task sets. In the present study, we set out to investigate the temporal dynamics of these agency-related processes (in task choice vs. no-choice conditions) using event-related brain potentials (ERPs). The results revealed agency-related modulations of a series of ERP components, including (1) an early parieto-occipital activation, taken to reflect the evaluation of choice versus no choice; (2) a subsequent medial frontal expression of the voluntary selection between task sets; (3) a CNV-like sustained negativity in preparation for the target; (4) a target-induced N210—P210 complex, taken to reflect early sensory-perceptual processing; and (5) a target-induced P3, associated with the evaluation of the stimulus and its designated response vis-à-vis the chosen versus competing task sets. Together, these results indicate that the opportunity to choose between tasks invokes activity originating from the medial frontal cortex, associated with voluntary task set selection, but also activation at different time points in a number of other brain areas, not necessarily captured by functional neuroimaging.     

On the representation of task information in task switching: Evidence from task and dimension switching

Task switching research has revealed that task changes lead to a performance switch cost. The present study focuses on the organization of task components in the task set. Three different views of task set organization have been distinguished and evidence in favor of each of these has been reported in the literature. In four experiments, we orthogonally varied the categorization task (magnitude and parity) and the stimulus dimension on which the categorization was to be made. Experiments 1, 2, and 4 used Stroop-like number stimuli, whereas Experiment 3 used global-local stimuli to define the stimulus dimension. In Experiments 2-4, the cue-stimulus interval was also varied. The findings showed that a change of any component resulted in a cost, without any reliable difference in the size of these costs. These results are consistent with the flat view on task-set organization, which assumes that the task set binds all elements in an unstructured representation, which is completely reconfigured each time a change to the task set is required. The implications of these findings are discussed in relation to other findings and the different views on task-set organization.     

Cognitive contributions of the ventral parietal cortex: an integrative theoretical account

Although ventral parietal cortex (VPC) activations can be found in a variety of cognitive domains, these activations have been typically attributed to cognitive operations specific to each domain. In this article, we propose a hypothesis that can account for VPC activations across all the cognitive domains reviewed. We first review VPC activations in the domains of perceptual and motor reorienting, episodic memory retrieval, language and number processing, theory of mind, and episodic memory encoding. Then, we consider the localization of VPC activations across domains and conclude that they are largely overlapping with some differences around the edges. Finally, we assess how well four different hypotheses of VPC function can explain findings in various domains and conclude that a bottom-up attention hypothesis provides the most complete and parsimonious account.     

Acute aerobic exercise and information processing: energizing motor processes during a choice reaction time task

The immediate and short-term after effects of a bout of aerobic exercise on young adults’ information processing were investigated. Seventeen participants performed an auditory two-choice reaction time (RT) task before, during, and after 40 min of ergometer cycling. In a separate session, the same sequence of testing was completed while seated on an ergometer without pedalling. Results indicate that exercise (1) improves the speed of reactions by energizing motor outputs; (2) interacts with the arousing effect of a loud auditory signal suggesting a direct link between arousal and activation; (3) gradually reduces RT and peaks between 15 and 20 min; (4) effects on RT disappear very quickly after exercise cessation; and (5) effects on motor processes cannot be explained by increases in body temperature caused by exercise. Taken together, these results support a selective influence of acute aerobic exercise on motor adjustment stage.     

Improving calibration without training: the role of task information

Medical students estimated probabilities that medical school applicants selected randomly from a defined population would be offered a place on the basis of information about eight characteristics of each one. Estimates were biased in favour of acceptance and this was unaffected by mere provision of base rate information. However, a first experiment showed that provision of this information reduced miscalibration after each candidate had been discussed within small groups of participants. A second experiment showed beneficial effects of providing people with the range of probability responses derived from a statistical model of how candidates' characteristics influenced whether or not they were offered a place. Numerical and graphical representations of this information both improved calibration but did so by having different effects on the distribution of participants' probability responses. Copyright © 2003 John Wiley & Sons, Ltd.     

Latent learning in a swimming pool place task by rats: Evidence for the use of associative and not cognitive mapping processes

Using a latent learning paradigm, the experiments examine two hypotheses of how rats solve place navigation tasks. According to associative theory, experience with all relevant cues is required for accurate navigation. According to cognitive mapping theory, animals can generate novel trajectories from knowledge of spatial relations of objects in the environment. Rats that had been placed on a platform, which was submerged in a pool of opaque water and was moved each day, were tested later for their ability to find the platform using only surrounding room cues. One 30-sec exposure to a platform location was effective in improving performance. Improvement was greatest when tests were given within minutes of placement, but facilitation was obtained for as long as 4 hr. Improved performance was obtained as soon as rats acquired the procedural aspects of the task but did not increase with subsequent practice. Improved performance was also obtained when pre-trained rats were tested in a novel environment. Despite the advantage conferred by exposure to the target platform, test swims were not accurate, placement-induced improvement was not as great as that following a single swimming trial, and placement combined with a swim resulted in best performance. The results suggest that rats use associative learning processes rather than cognitive mapping to solve place problems in a swimming pool.     

Endogenous BDNF is required for long-term memory formation in the rat parietal cortex

Information storage in the brain is a temporally graded process involving different memory phases as well as different structures in the mammalian brain. Cortical plasticity seems to be essential to store stable long-term memories, although little information is available at the moment regarding molecular and cellular events supporting memory consolidation in the neocortex. Brain-derived neurotrophic factor (BDNF) modulates both short-term synaptic function and activity-dependent synaptic plasticity in hippocampal and cortical neurons. We have recently demonstrated that endogenous BDNF in the hippocampus is involved in memory formation. Here we examined the role of BDNF in the parietal cortex (PCx) in short-term (STM) and long-term memory (LTM) formation of a one-trial fear-motivated learning task in rats. Bilateral infusions of function-blocking anti-BDNF antibody into the PCx impaired both STM and LTM retention scores and decreased the phosphorylation state of cAMP response element-binding protein (CREB). In contrast, intracortical administration of recombinant human BDNF facilitated LTM and increased CREB activation. Moreover, inhibitory avoidance training is associated with a rapid and transient increase in phospho-CREB/total CREB ratio in the PCx. Thus, our results indicate that endogenous BDNF is required for both STM and LTM formation of inhibitory avoidance learning, possibly involving CREB activation-dependent mechanisms. The present data support the idea that early sensory areas constitute important components of the networks subserving memory formation and that information processing in neocortex plays an important role in memory formation.     

Think-aloud protocols and the selection task: Evidence for relevance effects and rationalisation processes

Two experiments are reported that employed think-aloud methods to test predictions concerning relevance effects and rationalisation processes derivable from Evans' (1996) heuristic-analytic theory of the selection task. Evans' account proposes that card selections are triggered by relevance-determining heuristics, with analytic processing serving merely to rationalise heuristically cued decisions. As such, selected cards should be associated with more references to both their facing and their hidden sides than rejected cards, which are not subjected to analytic rationalisation. Experiment 1 used a standard selection-task paradigm, with negative components permuted through abstract conditional rules. Support was found for all heuristic-analytic predictions. This evidence was shown to be robust in Experiment 2, where “select - don't select” decisions were enforced for all cards. Both experiments also clarify the role played by secondary heuristics in cueing the consideration of hidden card values during rationalisation. We suggest that whilst Evans' heuristic-analytic model and Oaksford and Chater's (e.g., 2003) optimal data selection model can provide compelling accounts of our protocol findings, the mental models theory fares less well as an explanation of our full dataset.     

Playing the Simon game: Use of the Simon task for investigating human information processing

A little more than 40 years ago, J. R. Simon and colleagues introduced what is now called the Simon task, which yielded a correspondence effect known as the Simon effect. In this paper, I set Simon's contribution in the context of research on stimulus-response compatibility. The novel contribution of the Simon task is described, along with foundational findings using the task that Simon and colleagues reported. I acknowledge the significance of Simon's (1990) review chapter in generating my own interests in the Simon task and describe four selected lines of research from my lab that have been a result of those interests. The article concludes with a brief tribute to Simon and his contribution to experimental psychology.     

The contribution of the inferior parietal cortex to spoken language production

This functional MRI study investigated the involvement of the left inferior parietal cortex (IPC) in spoken language production (Speech). Its role has been apparent in some studies but not others, and is not convincingly supported by clinical studies as they rarely include cases with lesions confined to the parietal lobe. We compared Speech with non-communicative repetitive tongue movements (Tongue). The data were analyzed with both univariate contrasts between conditions and probabilistic independent component analysis (ICA). The former indicated decreased activity of left IPC during Speech relative to Tongue. However, the ICA revealed a Speech component in which there was correlated activity between left IPC, frontal and temporal cortices known to be involved in language. Therefore, although net synaptic activity throughout the left IPC may not increase above baseline conditions during Speech, one or more local systems within this region are involved, evidenced by the correlated activity with other language regions.     

Priming processes in the Simon task: more evidence from the lexical decision task for a third route in the Simon effect

Recently, it was proposed that the Simon effect would result not only from two interfering processes, as classical dual-route models assume, but from three processes. It was argued that priming from the spatial code to the nonspatial code might facilitate the identification of the nonspatial stimulus feature in congruent Simon trials. In the present study, the authors provide evidence that the identification of the nonspatial information can be facilitated by the activation of an associated spatial code. In three experiments, participants first associated centrally presented animal and fruit pictures with spatial responses. Subsequently, participants decided whether laterally presented letter strings were words (animal, fruit, or other words) or nonwords; stimulus position could be congruent or incongruent to the associated spatial code. As hypothesized, animal and fruit words were identified faster at congruent than at incongruent stimulus positions from the association phase. The authors conclude that the activation of the spatial code spreads to the nonspatial code, resulting in facilitated stimulus identification in congruent trials. These results speak to the assumption of a third process involved in the Simon task.     

Spatial conceptual influences on the coordination of bimanual actions: when a dual task becomes a single task

When the left and right hands produce 2 different rhythms simultaneously, coordination of the hands is difficult unless the rhythms can be integrated into a unified temporal pattern. In the present study, the authors investigated whether a similar account can be applied to the spatial domain. Participants (N = 8) produced a movement trajectory of semicircular form in single-limb and bimanual conditions. In the bimanual tasks, 1 limb moved above the other in the frontal plane. Bimanual unified tasks were constructed so that the spatial paths to be produced by the 2 limbs could be easily conceptualized as parts of a unified circle pattern. Bimanual distinct tasks availed a less obvious spatial pattern that would unify the 2 tasks, despite similar demands placed on the coordination dynamics in the 2 cases (e.g., the phase relations). The authors conclude that a dual task becomes a single task, and interlimb interference is reduced, when the spatial patterns produced by the 2 hands form a geometric arrangement that can be conceptualized as a unified representation.