Spatial localization in patients with unilateral posterior left or right hemisphere lesions

Visuospatial performance in patients with statistically-defined mild cognitive impairment

Introduction: The Oblique Effect denotes superior performance for perceiving horizontal or vertical rather than diagonal or oblique stimuli. The current research investigated responding to oblique test stimuli in patients with mild cognitive impairment (MCI).Method: Four statistically-determined groups (n = 112) were studied; patients with little to no cognitive impairment (non-MCI, n = 39); subtle cognitive impairment (SCI, n = 15); amnestic MCI (aMCI, n = 28); and a combined mixed/dysexecutive MCI (mixed/dys MCI, n = 30). The ability to respond to oblique versus non-oblique test stimuli was assessed using the Judgment of Line Orientation Test (JOLO). Comprehensive neuropsychological assessment was also obtained. Between-group differences for JOLO oblique and non-oblique test stimuli were analyzed. Hierarchical linear regression models were constructed to identify relations between accuracy for oblique and non-oblique test items and neurocognitive domains.Results: The mixed/dys MCI group demonstrated lower accuracy for oblique test items compared to non-MCI patients. Accurate responding to oblique test items was associated with better performance on tests measuring executive control, processing speed, naming/lexical retrieval, and verbal concept formation. No between-group differences were seen for non-oblique items and these items were not associated with cognition.Conclusions:Significant impairment on oblique test items distinguished patients with multi-domain/dysexecutive MCI from non-MCI patients. Accurate responding to oblique test items was associated with a complex array of neuropsychological tests suggesting that multidimensional neuropsychological skills underlie the visuospatial reasoning abilities necessary for successful oblique line identification. Research associating responding to oblique versus non-oblique test stimuli using additional neuropsychological test paradigms, and MRI-defined neuroanatomical regions of interest may provide additional information about the brain-behavior relations that underlie MCI subtypes.

Insights from neuropsychology: pinpointing the role of the posterior parietal cortex in episodic and working memory

The role of posterior parietal cortex (PPC) in various forms of memory is a current topic of interest in the broader field of cognitive neuroscience. This large cortical region has been linked with a wide range of mnemonic functions affecting each stage of memory processing: encoding, maintenance, and retrieval. Yet, the precise role of the PPC in memory remains mysterious and controversial. Progress in understanding PPC function will require researchers to incorporate findings in a convergent manner from multiple experimental techniques rather than emphasizing a particular type of data. To facilitate this process, here, we review findings from the human neuropsychological research and examine the consequences to memory following PPC damage. Recent patient-based research findings have investigated two typically disconnected fields: working memory (WM) and episodic memory. The findings from patient participants with unilateral and bilateral PPC lesions performing diverse experimental paradigms are summarized. These findings are then related to findings from other techniques including neurostimulation (TMS and tDCS) and the influential and more abundant functional neuroimaging literature. We then review the strengths and weaknesses of hypotheses proposed to account for PPC function in these forms of memory. Finally, we address what missing evidence is needed to clarify the role(s) of the PPC in memory.

Relationships between Constructional and Visuospatial Abilities in Normal Subjects and in Focal Brain-damaged Patients

We tested 125 normal subjects and 24 right and 22 left focal brain-damaged patients (RBD and LBD) on the Rey figure copying test and on a battery of perceptual and representational visuospatial tasks, in search of relationships between constructional and visuospatial abilities. Selected RBD and LBD were not affected by severe aphasia, unilateral spatial neglect or general intellectual defects. Both RBD and LBD showed defective performances on the constructional task with respect to normal subjects. As regards visuospatial tasks, both patient groups scored lower than normal subjects in judging angle width and mentally assembling geometrical figures; moreover, RBD, but not LBD, achieved scores significantly lower than healthy controls in judging line orientation and analyzing geometrical figures. Post-hoc comparisons did not reveal any significant differences between RBD and LBD. Multiple regression analysis showed that visuospatial abilities correlate with accuracy in copying geometrical drawings in normal subjects and in RBD, but not in LBD. From a theoretical perspective, these findings support the idea that visual perceptual and representational abilities do play a role in constructional skills.

Some surprising findings on the involvement of the parietal lobe in human memory

The posterior parietal lobe is known to play some role in a far-flung list of mental processes: linking vision to action (saccadic eye movements, reaching, grasping), attending to visual space, numerical calculation, and mental rotation. Here, we review findings from humans and monkeys that illuminate an untraditional function of this region: memory. Our review draws on neuroimaging findings that have repeatedly identified parietal lobe activations associated with short-term or working memory and episodic memory. We also discuss recent neuropsychological findings showing that individuals with parietal lobe damage exhibit both working memory and long-term memory deficits. These deficits are not ubiquitous; they are only evident under certain retrieval demands. Our review elaborates on these findings and evaluates various theories about the mechanistic role of the posterior parietal lobe in memory. The available data point towards the conclusion that the posterior parietal lobe plays an important role in memory retrieval irrespective of elapsed time. However, the available data do not support simple dichotomies such as recall versus recognition, working versus long-term memory. We conclude by formalizing several open questions that are intended to encourage future research in this rapidly developing area of memory research.

Is the posterior parietal lobe involved in working memory retrieval? Evidence from patients with bilateral parietal lobe damage

Neuroimaging evidence suggests that the parietal lobe has an important role in memory retrieval, yet neuropsychology is largely silent on this topic. Recently, we reported that unilateral parietal lobe damage impairs various forms of visual working memory when tested by old/new recognition. Here, we investigate whether parietal lobe working memory deficits are linked to problems at retrieval. We tested two patients with bilateral parietal lobe damage in a series of visual working memory tasks that probed recall and old/new recognition. Stimuli were presented sequentially and several stimulus categories were tested. The results of these experiments show that parietal lobe damage disproportionately impairs old/new recognition as compared to cued recall across stimulus categories. The observed performance dissociation suggests that the posterior parietal lobe plays a particularly vital role in working memory retrieval.

A general deficit of the 'automatic pilot' with posterior parietal cortex lesions?

Lesions of the parieto-occipital junction (POJ) in humans cause gross deviations of reaching movements and impaired grip formation if the targets are located in the subjects' peripheral visual field. Movements to central targets are typically less impaired. This disorder has been termed "optic ataxia". It has been suggested that a general deficit of online corrections under central as well as peripheral viewing conditions might be sufficient to explain this discrepancy. According to this hypothesis, patients with optic ataxia should demonstrate an impaired online correction of grip aperture under central viewing conditions if the target object changes its size during the grasping movement. We investigated this prediction in a patient with optic ataxia (I.G.) in a virtual visuo-haptic grasping task. We imposed an isolated need for online corrections of the hand aperture independently of positional changes of the target object. While we found some general inaccuracies of her grasping movements, the patient did not show a specific impairment of online adjustment of grip aperture. On the contrary, I.G. smoothly adjusted her grip aperture comparable to healthy subjects. A general deficit of fast movement correction affecting targets in peripheral as well as central visual fields thus does not appear to account for the overt visuomotor deficits in optic ataxia. Rather, it seems more likely that an anatomical dissociation between visuomotor pathways related to actions in the central and in the peripheral visual field underlies the dissociation of visuomotor performance depending on the retinotopic target position in optic ataxia.

Pointing to places and spaces in a patient with visual form agnosia

Previous investigations of visuospatial abilities in the visual form agnosic patient D.F. suggest that her egocentric sensorimotor processing is intact while her 'allocentric' judgments of spatial position are impaired. The current investigation extends these previous observations by comparing D.F.'s performance at pointing to a set of spatially distributed stimuli, either directly or by 'pantomiming' the responses in an adjacent homologous workspace. The results showed accurate sensorimotor localization when D.F. pointed directly to single targets or to sequences of targets, presumably as she could use egocentric visual coding. In spite of making relatively spared spatial judgments about the arrays, however, D.F. performed quite poorly when copying them and on the pantomimed pointing task. In this latter task good performance presumably depends on an ability to represent both the categorical and coordinate properties of the array (as does copying them), and to translate these into the effector-based coordinates required for accurate action. D.F.'s pantomimed pointing was similar to her copies of target arrays, as in both tasks there was evidence of spared (although somewhat degraded) appreciation of the relative spatial positions of the stimuli. Remarkably, her accuracy in this allocentric task was not worsened by longer pointing sequences. It is possible that D.F.'s degraded performance reflects a relative (though not complete) preservation of categorical coding within the ventral stream, despite a loss of coordinate coding there.

Lateralization of spatial-memory processes: evidence on spatial span, maze learning, and memory for object locations

Spatial memory is one of the most important cognitive functions in daily life, enabling us to locate objects in our environment or to learn a route or a path. In the present study, we elaborated on the hypothesis that human spatial memory consists of multiple sub-processes, relying on different brain structures. Therefore, 50 patients with an ischemic stroke and 40 healthy participants underwent tests measuring spatial span and maze learning. By means of a computer paradigm the following aspects of memory for object locations were assessed: (1) object location binding; (2) positional memory; (3) a combination of these two aspects. The results clearly showed a double dissociation: the group of patients with an infarct in the left hemisphere (LH) was impaired on object location binding, whereas the group with an infarct in the right hemisphere (RH) was impaired on positional memory. Lesions in the RH resulted also in impairments on maze learning. Moreover, patients with lesions in the posterior part of the parietal or the occipital lobe performed especially worse on spatial-memory tasks. These findings extend the theoretical framework of categorical versus coordinate spatial processing in the human brain and corroborate previous findings on selective aspects of memory for object locations.

Varieties of human spatial memory: a meta-analysis on the effects of hippocampal lesions

The current meta-analysis included 27 studies on spatial-memory dysfunction in patients with hippocampal damage. Each study was classified on the basis of the task that was used, i.e., maze learning, working memory, object-location memory, or positional memory. The overall results demonstrated impairments on all spatial-memory tasks. Clear differences in effect size were found between positional memory on the one hand and maze learning, object-location memory, and working memory on the other hand. Lateralization was found only on maze learning and object-location memory. These findings clearly indicate that specific aspects of spatial memory can be affected in various degrees in patients with hippocampal lesions. Moreover, these results strongly support the notion that the hippocampus is important in the processing of metric positional information, probably in the form of an allocentric cognitive map.