Loss of visual imagery: A generation deficit

Abstract

The case of a patient with an impairment in the ability both to generate visual images and to perform certain transformations upon visual images in reported. No impairment of long-term visual memory could be demonstrated, and the patient was able to perform various tasks on a perceptually derived image indicating that the visual buffer is probably intact. Either the patient has two distinct impairments: a generation deficit and transformation deficit, or these two problems are related and reflect an impairment of some form of imaged representation which is the repository both for images generated from long-term visual memory and for the images generated as a result of mental rotation on a perceptually given stimulus item. The imaged representation must be presumed to be distinct from the visual buffer. The case is also of interest since the patient (with a left hemisphere lesion) was impaired in mental rotations, a deficit typically associated with right hemisphere lesions.     

Common processing constraints for visuomotor and visual mental rotations

Naive human subjects were tested in three different tasks: (1) a visuomotor mental rotation task, in which the subjects were instructed to move a cursor at a given angle from a stimulus direction; (2) a visual mental rotation task, in which the subjects had to decide whether a displayed letter was normal or mirror image regardless of its orientation in the plane of presentation; and (3) a visuomotor memory scanning task, in which a list of two to five stimuli directions were presented sequentially and then one of the stimuli (test stimulus), except the last one, was presented again. Subjects were instructed to move a cursor in the direction of the stimulus that followed the test stimulus in the previous sequence. The processing rate of each subject in each task was estimated using the linear relation between the response time and the angle (mental rotation tasks) or the list length (memory scanning task). We found that the processing rates in the mental rotation tasks were significantly correlated but that neither correlated significantly with the processing rate in the memory scanning task. These results suggest that visuomotor and visual mental rotations share common processing constraints that cannot be ascribed to general mental processing performances. Correspondence to: A.P. Georgopoulos, Brain Sciences Center     

On the link between action planning and motor imagery: a developmental study

We examined the link between action planning and motor imagery in 6- and 8-year-old children. Action planning efficiency was assessed with a bar transport task. Motor imagery and visual imagery abilities were measured using a hand mental rotation task and a number (i.e., non-body stimuli) mental rotation task, respectively. Overall, results showed that performance varied with age in all tasks, performance being progressively refined with development. Importantly, action planning performance was correlated with motor imagery, whereas no relationship was evident between action planning and visual imagery at any age. The results showed that the ability to engage sensorimotor mechanisms when solving a motor imagery task was concomitant with action planning efficiency. The present work is the first demonstration that evaluating the consequences of the upcoming action in grasping depends on children’s abilities to mentally simulate the response options to choose the most efficient grasp.     

Mental transformation abilities in patients with unilateral and bilateral vestibular loss

Vestibular information helps to establish a reliable gravitational frame of reference and contributes to the adequate perception of the location of one’s own body in space. This information is likely to be required in spatial cognitive tasks. Indeed, previous studies suggest that the processing of vestibular information is involved in mental transformation tasks in healthy participants. In this study, we investigate whether patients with bilateral or unilateral vestibular loss show impaired ability to mentally transform images of bodies and body parts compared to a healthy, age-matched control group. An egocentric and an object-based mental transformation task were used. Moreover, spatial perception was assessed using a computerized version of the subjective visual vertical and the rod and frame test. Participants with bilateral vestibular loss showed impaired performance in mental transformation, especially in egocentric mental transformation, compared to participants with unilateral vestibular lesions and the control group. Performance of participants with unilateral vestibular lesions and the control group are comparable, and no differences were found between right- and left-sided labyrinthectomized patients. A control task showed no differences between the three groups. The findings from this study substantiate that central vestibular processes are involved in imagined spatial body transformations; but interestingly, only participants with bilateral vestibular loss are affected, whereas unilateral vestibular loss does not lead to a decline in spatial imagery.     

The nature of imagery processes underlying food cravings

Objective. The study used a working memory approach to examine the nature of the imagery processes underlying food cravings. Design and method. A sample of 60 dieters and 60 non‐dieters were asked to imagine either a food induction or a holiday induction scenario. Participants then performed 18 trials of either a visual imagery task (loading the visuo‐spatial sketch pad) or auditory imagery task (loading the phonological loop). Food craving was measured before and after the induction scenario, and then after every 6 trials of the imagery task. Results. Craving intensity increased following instructions to imagine the food (but not holiday) induction scenario, especially for dieters. As predicted, the visual imagery task was superior to the auditory imagery task in reducing the level of food craving. Discussion. The results confirmed the imaginal basis of food cravings. Specifically, they demonstrated that the imagery processes involved in food cravings are predominantly visual in nature. Hence concurrent tasks that load the visuospatial sketch pad of working memory can be used to reduce food cravings. The findings have potential application in the treatment of craving episodes in clinical populations.     

Impaired memory for faces and social scenes in autism: clinical implications of memory dysfunction.

A clinical memory test, the Wechsler Memory Scale-III (WMS-III), was used to study the auditory and visual memory of 29 high-functioning adults with autism and 34 group-matched normal controls. The individuals with autism performed as well as the controls on immediate and delayed memory for word pairs and stories and on a verbal working memory task. The autism group was impaired on immediate and delayed recall of faces and of family scenes and had impaired spatial working memory. The integrity of verbal working memory and impaired spatial working memory is consistent with the findings of other studies and may reflect the greater computational demands of the spatial task. Most importantly, the deficits in memory for faces and common social scenes, complex visual/spatial stimuli, demonstrate the contribution of memory dysfunction in autism to deficits in real life function.     

Cholinergic blockade effects on spatial integration versus cue discrimination performance

A within-subjects investigation was conducted to determine the effects of central versus peripheral cholinergic blockade in animals tested either on a spatial integration task in which the possibility of rule learning was also available or on a visual discrimination task in which the daily location of food was marked by a distinctive visual stimulus pattern. All testing was conducted on the Maier three-table apparatus. It was found that the only effect of the peripheral cholinergic blockade on the performance of either task group was to produce a decrease in exploratory behavior. In contrast, central cholinergic blockade markedly impaired spatial integration performance; however, it did not impair the ability of animals in rule learning or visual discrimination learning. It was also found that central cholinergic blockade impaired the animal's tendency to enter all tables before reentering a given table during the exploratory phase of the daily session. This finding was interpreted as reflecting an impairment of working memory for spatial information, rather than a general impairment in working memory, and this interpretation was applied to the explanation of the deficit in the spatial integration performance.     

Spatial memory dissociations in mice lacking GluR1

Gene-targeted mice lacking the AMPA receptor subunit GluR1 (GluR-A) have deficits in hippocampal CA3-CA1 long-term potentiation. We now report that they showed normal spatial reference learning and memory, both on the hidden platform watermaze task and on an appetitively motivated Y-maze task. In contrast, they showed a specific spatial working memory impairment during tests of non-matching to place on both the Y-maze and an elevated T-maze. In addition, successful watermaze and Y-maze reference memory performance depended on hippocampal function in both wild-type and mutant mice; bilateral hippocampal lesions profoundly impaired performance on both tasks, to a similar extent in both groups. These results suggest that different forms of hippocampus-dependent spatial memory involve different aspects of neural processing within the hippocampus.     

Impaired Imagery for Upper Limbs

The brain processes associated with mental imagery have long been a matter of debate. Neuroimaging and neuropsychological studies have yielded diverging evidence of mental transformation activating the right hemisphere, the left hemisphere, or both. Here, using a mirror/normal discrimination task with rotated body parts (BPs) and external objects (EOs), we describe the case of a patient who developed a selective deficit in mental imagery of such BPs due to left posterior parietal brain damage. In addition, the patient’s deficit predominated for pictures of right arms (i.e., arms corresponding to the patient’s imagined contralesional arm) and was further characterised by an inability to distinguish between anatomically possible and impossible arm positions. This neuropsychological deficit was corroborated by neuroimaging evidence revealing the absence of activation in the left parietal lobe for the mental rotation of body parts as shown in healthy participants. In contrast, his behavioural performance and brain activation for EOs were similar to those of healthy participants. These data suggest that mental imagery of BPs and EOs relies on different cognitive and neural mechanisms and indicate that the left posterior parietal lobe is a necessary structure for mental transformations of human BPs.     

Hippocampal function required for nonspatial working memory

Summary The hippocampus has been implicated as a brain structure necessary for normal memory functions and normal spatial behavior. Both these explanations are consistent with the results of previous experiments demonstrating an impairment of choice accuracy following fimbria-fornix lesions on an elevated radial arm maze because the test procedure required working memory and permitted cognitive mapping. In the present experiment, rats were tested in an enclosed radial arm maze in which each arm had a distinctive set of discriminative stimuli and the test procedure required working memory but prevented cognitive mapping. Rats were tested preoperatively, given fimbria-fornix lesions, and then tested postoperatively. The rats with lesions performed at chance levels and showed no evidence of recovery of function. These results are consistent with the hypothesis that the poor choice accuracy in the elevated radial arm maze task arose because of the working memory requirements of that task, rather than its cognitive mapping characteristics, and support interpretations of hippocampal function that emphasize memory processing.The research described here was supported in part by a Research Grant MH 24213 from the National Institute of Mental Health and by a Biomedical Research Support Grant from the Johns Hopkins University     

Study of verbal working memory in patients with Parkinson's disease

The authors examined the nature of the working memory deficit in persons with Parkinson's disease (PD). Three hypotheses were tested: a limited storage capacity, an impaired executive component, and a reduction of psychomotor speed. Verbal working memory was assessed in 14 PD patients without dementia and 14 matched control participants. Participants were administered a classical verbal span test, working memory tasks that required either updating or manipulation capacities, and motor and psychomotor speed tasks. Patients' performance was comparable to that of control participants on the verbal span test. However, results on the working memory tasks indicated a deficit in manipulation with normal updating capacities. Motor and psychomotor slowing were found in the patient group, but slowing could not fully account for the impairment observed in the manipulation task. Results indicated that there is a genuine but selective working memory impairment in patients with PD.     

Working memory in aged rats

The performances of young and aged rats were compared on a spatial (spatial delayed nonmatching-to-sample) and a nonspatial (object delayed nonmatching-to-sample) test of working memory. Although evidence was found that aging showed acquisition of both of these tasks, performance over different retention intervals of up to 60 s was normal once the task was mastered. An impairment was found, however, in the performance of the spatial test when the number of locations to be remembered on each trial was increased from one to two. The conclusions of this study are that under some conditions, the retention capabilities of aged rats may not change and that some acquisition impairments do not reflect alterations in learning or memory per se, but, in common with other studies, deficits in the remembrance of spatial locations may be found.     

Deletion of the Coffin–Lowry Syndrome Gene Rsk2 in Mice is Associated With Impaired Spatial Learning and Reduced Control of Exploratory Behavior

Coffin–Lowry Syndrome (CLS) is an X-linked syndromic form of mental retardation associated with skeletal abnormalities. It is caused by mutations of the Rsk2 gene, which encodes a growth factor regulated kinase. Gene deletion studies in mice have shown an essential role for the Rsk2 gene in osteoblast differentiation and function, establishing a causal link between Rsk2 deficiency and skeletal abnormalities of CLS. Although analyses in mice have revealed prominent expression of Rsk2 in brain structures that are essential for learning and memory, evidence at the behavioral level for an involvement of Rsk2 in cognitive function is still lacking. Here, we have examined Rsk2-deficient mice in two extensive batteries of behavioral tests, which were conducted independently in two laboratories in Zurich (Switzerland) and Orsay (France). Despite the known reduction of bone mass, all parameters of motor function were normal, confirming the suitability of Rsk2-deficient mice for behavioral testing. Rsk2-deficient mice showed a mild impairment of spatial working memory, delayed acquisition of a spatial reference memory task and long-term spatial memory deficits. In contrast, associative and recognition memory, as well as the habituation of exploratory activity were normal. Our studies also revealed mild signs of disinhibition in exploratory activity, as well as a difficulty to adapt to new test environments, which likely contributed to the learning impairments displayed by Rsk2-deficient mice. The observed behavioral changes are in line with observations made in other mouse models of human mental retardation and support a role of Rsk2 in cognitive functions. Edited by Andrew Holmes     

Mental rotation task of hands: differential influence number of rotational axes

Various studies on the hand laterality judgment task, using complex sets of stimuli, have shown that the judgments during this task are dependent on bodily constraints. More specific, these studies showed that reaction times are dependent on the participant’s posture or differ for hand pictures rotated away or toward the mid-sagittal plane (i.e., lateral or medial rotation, respectively). These findings point to the use of a cognitive embodied process referred to as motor imagery. We hypothesize that the number of axes of rotation of the displayed stimuli during the task is a critical factor for showing engagement in a mental rotation task, with an increased number of rotational axes leading to a facilitation of motor imagery. To test this hypothesis, we used a hand laterality judgment paradigm in which we manipulated the difficulty of the task via the manipulation of the number of rotational axes of the shown stimuli. Our results showed increased influence of bodily constraints for increasing number of axes of rotation. More specifically, for the stimulus set containing stimuli rotated over a single axis, no influence of biomechanical constraints was present. The stimulus sets containing stimuli rotated over more than one axes of rotation did induce the use of motor imagery, as a clear influence of bodily constraints on the reaction times was found. These findings extend and refine previous findings on motor imagery as our results show that engagement in motor imagery critically depends on the used number of axes of rotation of the stimulus set.     

A deficit in attentional set-shifting of violent offenders

BACKGROUND: Recent brain imaging studies suggest that proneness to violence and antisocial behaviour may be associated with dysfunction of the prefrontal cortex. The present study. therefore, examined aspects of prefrontally guided executive functions in a group of criminal violent men. METHODS: Violent offenders undergoing forensic psychiatric examination by court order undertook computerized tasks for planning, visual working memory and attentional set-shifting from the Cambridge Neuropsychological Test Automated Battery. Their performance was compared to that of subjects with marginal mental retardation and normal controls. RESULTS: Violent offenders performed well on tasks for spatial and figurative working memory, as well as on a test for planning. A marked impairment was observed in the attentional set-shifting task: offenders made significantly more errors than the other groups when required to shift attention from one perceptual dimension to another. Reversal learning was also deficient. Correlational analyses within the offender group revealed that poor performance on the perceptual shift problem was associated with fewer errors in tasks for working memory and planning. CONCLUSIONS: The present results suggest that violent offenders show dual impairments in inhibitory cognitive control. First, they are deficient in shifting attention from one category to another. Secondly, the ability to alter behaviour in response to fluctuations in the emotional significance of stimuli is compromised. These deficits might constitute cognitive reflections of the biological prefrontal alterations observed in this group of people.     

Negative BOLD in Sensory Cortices During Verbal Memory: A Component in Generating Internal Representations?

People tend to close their eyes when trying to retrieve an event or a visual image from memory. However the brain mechanisms behind this phenomenon remain poorly understood. Recently, we showed that during visual mental imagery, auditory areas show a much more robust deactivation than during visual perception. Here we ask whether this is a special case of a more general phenomenon involving retrieval of intrinsic, internally stored information, which would result in crossmodal deactivations in other sensory cortices which are irrelevant to the task at hand. To test this hypothesis, a group of 9 sighted individuals were scanned while performing a memory retrieval task for highly abstract words (i.e., with low imaginability scores). We also scanned a group of 10 congenitally blind, which by definition do not have any visual imagery per se. In sighted subjects, both auditory and visual areas were robustly deactivated during memory retrieval, whereas in the blind the auditory cortex was deactivated while visual areas, shown previously to be relevant for this task, presented a positive BOLD signal. These results suggest that deactivation may be most prominent in task-irrelevant sensory cortices whenever there is a need for retrieval or manipulation of internally stored representations. Thus, there is a task-dependent balance of activation and deactivation that might allow maximization of resources and filtering out of non relevant information to enable allocation of attention to the required task. Furthermore, these results suggest that the balance between positive and negative BOLD might be crucial to our understanding of a large variety of intrinsic and extrinsic tasks including high-level cognitive functions, sensory processing and multisensory integration.     

Working memory impairment and reduced hippocampal and prefrontal cortex c-Fos expression in a rat model of cirrhosis

Hepatic encephalopathy (HE) is a frequent neurological complication observed in patients with liver malfunction. Previous studies have shown memory impairment in these patients. In order to investigate brain substrates of spatial working memory impairment in chronic HE, neuronal expression of c-Fos protein was studied in an experimental model of cirrhosis. Control and cirrhotic rats were trained on a spatial working memory task in the Morris water maze (MWM). Differences between groups were found in the working memory task. Cirrhotic rats were unable to locate the platform in the retention trial. Neuronal activation, measured by c-Fos protein, was compared between groups. No differences were found in c-Fos expression of control and cirrhotic rats that were not tested in the MWM. Working memory task produced increase in c-Fos positive cells in dorsal hippocampus, CA1 and CA3, and prefrontal cortex in control group compared to thioacetamide group or naïve, which only swam in the maze during a similar time. These findings suggest that cirrhotic rats show spatial working memory impairment that could be linked to dysfunction in neuronal activity in prefrontal cortex and hippocampus.     

Inhibition of orienting during a memory-guided saccade task shows a Mexican-hat distribution

Recent behavioral studies in monkeys and humans have shown that holding an item in spatial working memory may lead to sustained and spatially selective prolongation of reaction times (RTs) to visual stimuli presented during the memory delay. In order to resolve the seeming contradiction between these findings and current theories on the interaction of working memory and attentional orienting, it has been hypothesized that memory-dependent modulation of orienting may be the net effect of superposed facilitatory and inhibitory mechanisms. Their relative strength during the memory delay may determine whether RTs to visual stimuli presented during the memory delay are shortened or prolonged. Here, we expand on this hypothesis by investigating the spatial distribution of memory-dependent inhibition with behavioral data from normal human subjects. The experiment consisted of a combination of an oculomotor spatial working memory task (memory-guided saccade task, 6-s delay) and a visual discrimination task (performed 1500, 2500, or 3500 ms after presentation of the memory cue). RTs to discrimination stimuli were analyzed as a function of memory-guided saccade amplitude. By fitting polynomial approximations to our data we show that the spatial distribution of memory-dependent inhibition of orienting significantly differs from a monotonic gradient across the visual field. Instead, we demonstrate the existence of a central inhibitory peak surrounded by a facilitatory annulus, forming a transient "inverted Mexican hat" profile, which mirror-images findings from recent studies on the spatial distribution of attention. These findings are consistent with the hypothesis of a highly flexible modulation of orienting in which both the signs and spatial distribution of memory-dependent bias signals are adapted to behavioral demands.     

The alpha2 agonist, clonidine, improves spatial working performance in Parkinson's disease.

Previous work has shown that the dopaminergic defect in Parkinson's disease is involved, to some extent, in the "frontal"-like impairment in spatial working memory and attentional set-shifting functions. We investigated whether an alpha2 agonist, clonidine (0.5 and 2 microg/kg, per os), could alleviate spatial working memory and attentional set-shifting defect in Parkinson's disease patients. We observed that 2 microg/kg clonidine stimulated spatial working memory accuracy, but had no effect on attentional set shifting or visual recognition memory. Clonidine was also effective in stimulating spatial working memory after withdrawal of dopaminergic drugs, and when this was done, its effect was greater in severe Parkinson's disease patients. In contrast, clonidine failed to stimulate visual recognition memory. These results suggest that disrupted activation of alpha2 adrenoceptors may contribute to the impairment of spatial working memory in Parkinson's disease.     

Impairment of olfactory identification in obsessive-compulsive disorder

BACKGROUND: Olfactory identification ability has been associated with processing in the orbitofrontal cortex (OFC), an area that has been implicated in the pathophysiology of obsessive-compulsive disorder (OCD). Although olfactory sensitivity is normal in patients with OCD, no study has investigated olfactory identification in this disorder. METHODS: A group of 20 subjects with OCD and 23 age- and education-matched controls performed a standardized test of olfactory identification. They also performed computerized tests of spatial memory span, spatial working memory and spatial recognition memory that have been shown previously to be sensitive to cognitive deficits in patients with OCD. RESULTS: Performance on the olfactory identification task, spatial recognition task and spatial span task was significantly worse in the OCD group than controls. CONCLUSIONS: While impairment in spatial cognition is consistent with previous studies of OCD, its significance for brain-behaviour models of OCD is unclear. However, the finding of abnormal olfactory identification in patients with OCD is consistent with the hypothesis that there is a disruption to processing at the level of the OFC in the disorder.