Tomaso Vecchi

Neural correlates of spatial working memory in humans: A functional magnetic resonance imaging study comparing visual and tactile processes

Recent studies of neural correlates of working memory components have identified both low-level perceptual processes and higher-order supramodal mechanisms through which sensory information can be integrated and manipulated. In addition to the primary sensory cortices, working memory relies on a widely distributed neural system of higher-order association areas that includes posterior parietal and occipital areas, and on prefrontal cortex for maintaining and manipulating information. The present study was designed to determine brain patterns of neural response to the same spatial working memory task presented either visually or in a tactile format, and to evaluate the relationship between spatial processing in the visual and tactile sensory modalities. Brain activity during visual and tactile spatial working memory tasks was measured in six young right-handed healthy male volunteers by using functional magnetic resonance imaging. Results indicated that similar fronto-parietal networks were recruited during spatial information processing across the two sensory modalities-specifically the posterior parietal cortex, the dorsolateral prefrontal cortex and the anterior cingulate cortex. These findings provide a neurobiological support to behavioral observations by indicating that common cerebral regions subserve generation of higher order mental representations involved in working memory independently from a specific sensory modality.

Imagery and spatial processes in blindness and visual impairment.

The objective of this review is to examine and evaluate recent findings on cognitive functioning (in particular imagery processes) in individuals with congenital visual impairments, including total blindness, low-vision and monocular vision. As one might expect, the performance of blind individuals in many behaviours and tasks requiring imagery can be inferior to that of sighted subjects; however, surprisingly often this is not the case. Interestingly, there is evidence that the blind often employ different cognitive mechanisms than sighted subjects, suggesting that compensatory mechanisms can overcome the limitations of sight loss. Taken together, these studies suggest that the nature of perceptual input on which we commonly rely strongly affects the organization of our mental processes. We also review recent neuroimaging studies on the neural correlates of sensory perception and mental imagery in visually impaired individuals that have cast light on the plastic functional reorganization mechanisms associated with visual deprivation.

Gender differences in visuo-spatial processing: the importance of distinguishing between passive storage and active manipulation.

The study here reported investigates the hypothesis that gender differences in visuo-spatial abilities are mainly confined to active processing tasks. Male and female participants were required to perform passive tasks involving the recall of previously memorized positions within matrices of different sizes, as well as active tasks in which they had to mentally follow a pathway in the same matrices. The results confirmed that male superiority became evident as the active processing requirements increased while only marginal gender difference was reported in passive tasks. To strengthen the specific role of the active-passive distinction in identifying gender differences, confounding factors such as type of material and use of verbal strategies were ruled out. These findings, in line with a number of studies on individual differences, high-light the importance of addressing visuo-spatial ability as a multicomponential cognitive function which entails different type of visuo-spatial processing or mechanisms (i.e., active processing and passive storage of information) rather than as a unitary concept.

Do We Really Need Vision? How Blind People “See” the Actions of Others

Observing and learning actions and behaviors from others, a mechanism crucial for survival and social interaction, engages the mirror neuron system. To determine whether vision is a necessary prerequisite for the human mirror system to develop and function, we used functional magnetic resonance imaging to compare brain activity in congenitally blind individuals during the auditory presentation of hand-executed actions or environmental sounds, and the motor pantomime of manipulation tasks, with that in sighted volunteers, who additionally performed a visual action recognition task. Congenitally blind individuals activated a premotor–temporoparietal cortical network in response to aurally presented actions that overlapped both with mirror system areas found in sighted subjects in response to visually and aurally presented stimuli, and with the brain response elicited by motor pantomime of the same actions. Furthermore, the mirror system cortex showed a significantly greater response to motor familiar than to unfamiliar action sounds in both sighted and blind individuals. Thus, the mirror system in humans can develop in the absence of sight. The results in blind individuals demonstrate that the sound of an action engages the mirror system for action schemas that have not been learned through the visual modality and that this activity is not mediated by visual imagery. These findings indicate that the mirror system is based on supramodal sensory representations of actions and, furthermore, that these abstract representations allow individuals with no visual experience to interact effectively with others.

Aging and everyday memory: the beneficial effect of memory training

The authors investigated elderly peoples ability to benefit from specific memory training. Empirical evidence of cognitive aging shows a deterioration in working memory ability but also suggests that elderly people maintain the ability to acquire new information and strategies. The aim of the present study was to investigate the effects of two different mnemonic strategies (Loci mnemonic vs. Strategic training) in young and older adults and to evaluate the ability of the older groups to improve performance. Participants received extensive practice in the use of a specific strategy. Three groups of participants (20 adult, 20 younger elderly, and 20 older elderly) were tested in the laboratory, as well as in ecological conditions using a battery of cognitive tests. Questionnaires were also administrated to explore cognitive, metacognitive and emotive motivational aspects of working memory performance. The results show the efficacy of both trainings in improving performances in different tasks, particularly the ecological. The elderly benefit from strategies as much as younger people; nevertheless, the memory performances of the latter are higher. Differences between the two trainings are found only in the task evaluating ability to re-use learnt strategies in other unfamiliar situations. Improvement in performance was more pronounced for the strategic training.

Passive Storage and Active Manipulation in Visuo-spatial Working Memory: Further Evidence From the Study of Age Differences

Recent theoretical accounts of working memory proposed a distinction between passive storage and active processing of visuo-spatial information. These hypotheses are based on empirical evidence showing that individual differences in visuo-spatial abilities are frequently modulated by this variable. However, results from age differences studies are not clear, and this research was designed to specifically investigate the level of competence of elderly people in tasks measuring visuo-spatial working memory and, in particular, passive and active components of the system. Three groups of participants (mean ages were approximately 22, 66, and 76) were tested in eight cognitive tasks tapping passive storage and active manipulation in various aspects of visuo-spatial and verbal processing. Results showed that elderly people are selectively impaired in active tasks, and these tasks were also more sensitive in detecting differences within the older group. These data highlight the need for theoretical models of wor...

Visuo-spatial working memory: Structures and variables affecting a capacity measure

The present paper examines the issue of the capacity of visuo-spatial working memory. A series of experiments test the hypothesis that two different components are critical in visuo-spatial working memory (passive store and active imagery operations), and, thereafter, attempt to specify the variables that affect the capacity of the passive store component. In the experiments, congenitally blind and sighted participants were asked to remember the spatial positions of target objects in two-dimensional matrices, with or without simultaneously performing a sequence of spatially-based imagery operations. We considered both the positions recall performance (the passive storage component) and the sequential imagery processing performance (the active processing component). We suggest that the two components of visuo-spatial working memory are independent. We also propose that both the number of relevant matrices and the number of target objects within each matrix affect the capacity of visuo-spatial working memory, with the latter factor possibly playing a greater role than the former one.

Visuo-spatial imagery in congenitally totally blind people.

The present study provides evidence for congenitally blind peoples ability to generate visuo-spatial images, and explores its limitations. Congenitally blind and sighted participants were asked to memorize the spatial positions of target objects (cubes) in two- and three-dimensional matrices, while simultaneously performing a sequence of spatially based imagery operations. Furthermore, during half of the trials, subjects were required to perform an articulatory suppression task. Although articulatory suppression affected both groups to the same extent, congenitally blind people performed poorly with more demanding spatial tasks and when an active elaboration was required.

Contrasting early visual cortical activation states causally involved in visual imagery and short‐term memory

Whether visual imagery and visual short‐term memory (STM) share the same neural resources, and the extent to which the early visual cortex (V1/V2) is involved in these processes, has been the subject of much debate. Here, we used transcranial magnetic stimulation (TMS) in two separate experiments to contrast the neural states associated with visual imagery and visual STM in the early visual cortex. In Experiment 1, we investigated V1/V2 activation states at the end of the retention phase in a visual imagery and a visual STM task. V1/V2 TMS facilitated performance in both tasks; the finding that imagery and STM interacted with TMS in the same way suggests that the two processes have similar effects on early visual cortical excitability. In Experiment 2, we investigated V1/V2 activation states at the beginning of the retention phase. V1/V2 TMS impaired performance in the visual STM task, whereas it had no effect on the imagery task. Taken together, our findings show that the late phases of the early visual cortical activation state associated with visual imagery and visual STM are similar; differences between the two processes are apparent in the early phases of the tasks. Our results also suggest that the causal role of the early visual cortex in visual STM includes both the initial translation of the visual input into working memory and the subsequent maintenance of the mental representation. Finally, our findings indicate that visual STM sensory recruitment in working memory might act via excitability modulation of V1/V2 neurons.

Using state‐dependency of transcranial magnetic stimulation (TMS) to investigate letter selectivity in the left posterior parietal cortex: a comparison of TMS‐priming and TMS‐adaptation paradigms

The state‐dependency of transcranial magnetic stimulation (TMS) can be used to investigate the neural properties of subregions of the stimulated region. The objective of the present study was to determine whether state‐dependency can reveal letter selectivity in the left posterior parietal cortex (PPC), a region known to contain letter‐selective neurons. In two experiments, we used visual priming and adaptation to modulate the initial activation state of the left PPC prior to application of TMS. In the priming experiment, TMS was applied over the left PPC during the delay between the prime and the target stimulus on each experimental trial. Left PPC TMS reversed the effects of priming by facilitating the detection of non‐primed letters, whereas detection of primed letters was unaffected. As neurons tuned to non‐primed letters were less active at the time of TMS application than neurons tuned to the primed letters, this finding demonstrates that TMS preferentially facilitates the detection of attributes encoded by the less active neural populations. A similar facilitation of the less active neural populations was observed when adaptation was used to suppress letter‐selective neurons prior to application of TMS. Our study demonstrates that TMS‐priming and TMS‐adaptation paradigms can reveal letter selectivity in the left PPC and thus be useful in the study of language processes. Our results also show that the state‐dependent TMS effects obtained with visual priming are similar to those found with TMS adaptation: in both cases, attributes encoded by the less active neural populations are preferentially facilitated.