A walk on the dark side: TMS over the right inferior frontal gyrus (rIFG) disrupts behavioral responses to infant stimuli.

Infant signals, including infant sounds and facial expressions, play a critical role in eliciting parental proximity and care. Processing of infant signals in the adulthood brain is likely to recruit emotional empathy neural circuits, including the inferior frontal gyrus (IFG). Here, we used transcranial magnetic stimulation (TMS) to test the role of right IFG (rIFG) in behavioral responses to infant signals. Specifically, a group of nulliparous women were asked to perform a handgrip dynamometer task and an Approach-Avoidance Task (AAT) after receiving TMS over the right IFG or over a control site (vertex). Suppressing activity in the rIFG affected the modulation of handgrip force in response to infant crying. Moreover, the AAT showed that participants tend to avoid the sad infant face after Vertex stimulation, and this bias was counteracted by rIFG stimulation. Our results suggest a causal role of rIFG in sensitive responding towards sad infants and point to the rIFG as a critical node in the neural network underlying the innate releasing mechanism for feelings of love, affection and caring of sad infants.

The Spatial Musical Association of Response Codes does not depend on a normal visual experience: A study with early blind individuals.

Converging evidence suggests that the perception of auditory pitch exhibits a characteristic spatial organization. This pitch-space association can be demonstrated experimentally by the Spatial Musical Association of Response Codes (SMARC) effect. This is characterized by faster response times when a low-positioned key is pressed in response to a low-pitched tone, and a high-positioned key is pressed in response to a high-pitched tone. To investigate whether the development of this pitch-space association is mediated by normal visual experience, we tested a group of early blind individuals on a task that required them to discriminate the timbre of different instrument sounds with varying pitch. Results revealed a comparable pattern in the SMARC effect in both blind participants and sighted controls, suggesting that the lack of prior visual experience does not prevent the development of an association between pitch height and vertical space.

Happiness takes you right: the effect of emotional stimuli on line bisection.

Emotion recognition is mediated by a complex network of cortical and subcortical areas, with the two hemispheres likely being differently involved in processing positive and negative emotions. As results on valence-dependent hemispheric specialisation are quite inconsistent, we carried out three experiments with emotional stimuli with a task being sensitive to measure specific hemispheric processing. Participants were required to bisect visual lines that were delimited by emotional face flankers, or to haptically bisect rods while concurrently listening to emotional vocal expressions. We found that prolonged (but not transient) exposition to concurrent happy stimuli significantly shifted the bisection bias to the right compared to both sad and neutral stimuli, indexing a greater involvement of the left hemisphere in processing of positively connoted stimuli. No differences between sad and neutral stimuli were observed across the experiments. In sum, our data provide consistent evidence in favour of a greater involvement of the left hemisphere in processing positive emotions and suggest that (prolonged) exposure to stimuli expressing happiness significantly affects allocation of (spatial) attentional resources, regardless of the sensory (visual/auditory) modality in which the emotion is perceived and space is explored (visual/haptic).

Cross-adaptation combined with TMS reveals a functional overlap between vision and imagery in the early visual cortex.

The extent to which the generation of mental images draws on the neuronal representations involved in visual perception has been the subject of much debate. To investigate this overlap, we assessed whether adaptation to visual stimuli affects the ability to generate visual mental images; such cross-adaptation would indicate shared neural representations between visual perception and imagery. Mental imagery was tested using a modified version of the clock task, in which subjects are presented with a digital time (e.g. "2.15") and are asked to generate a mental image of the clock hands displaying this time on an empty clock face. Participants were adapted to oriented lines either on the upper or lower side of the clock face prior to the mental image generation. The results showed that mental imagery was impaired when the mental image had to be generated in the adapted region of visual space (Experiment 1). In Experiment 2, we used TMS to determine whether this adaptation effect occurs in the early visual cortex (EVC; V1/V2). Relative to control conditions (No TMS and Vertex TMS), EVC TMS facilitated mental imagery generation when the mental image spatially overlapped with the adapter. Our results thus show that neuronal representations in the EVC which encode (and are suppressed by) visual input play a causal role in visual mental imagery.

Modulation of visual cortical excitability by working memory: effect of luminance contrast of mental imagery.

Although much is known about the impact of stimulus properties such as luminance contrast, spatial frequency, and orientation on visually evoked neural activity, much less is known about how they modulate neural activity when they are properties of a mental image held in working memory (WM). Here we addressed this question by investigating how a parametric manipulation of an imagined stimulus attribute affects neuronal excitability in the early visual cortex. We manipulated luminance contrast, a stimulus property known to strongly affect the magnitude of neuronal responses in early visual areas. Luminance contrast modulated neuronal excitability, as assessed by the frequency of phosphenes induced by transcranial magnetic stimulation (TMS) with the exact nature of this modulation depending on TMS intensity. These results point to a strong overlap in the neuronal processes underlying visual perception and mental imagery: not only does WM maintenance selectively engage neurons which are tuned to the maintained attribute (as has previously been shown), but the extent to which those neurons are activated depends on the image contrast (as is the case with visually evoked responses). From a methodological viewpoint, these results suggest that assessment of visual cortical excitability using TMS is affected by the TMS intensity used to probe the neuronal population.

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.

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.

Supramodality effects in visual and haptic spatial processes.

In this article, the authors investigated unimodal and cross-modal processes in spatial working memory. A number of locations had to be memorized within visual or haptic matrices according to different experimental conditions known to be critical in accounting for the effects of perception on imagery. Results reveal that some characteristics of the generated mental image remained strictly inherent to the modality in which information was acquired; in general, accuracy was higher when configurations were visually rather than haptically explored (Experiments 1 and 3). Interestingly, the same pattern emerged when the effects of simultaneous versus sequential processing of the stimuli inherent to vision and haptics were isolated from perceptual modality (Experiment 2). Supramodal elements were also identified (Experiment 3) that were specifically associated to the nature of the cognitive processes, regardless of the original characteristics of the sensory information. These data indicate that both unimodal modality-specific and higher order supramodal mechanisms are simultaneously used in spatial processes.

Effects of late visual impairment on mental representations activated by visual and tactile stimuli.

Similarly to sighted people, individuals congenitally affected by a severe visual impairment can maintain and mentally manipulate spatial information about tactile stimuli [Vecchi, T., Cattaneo, Z., Monegato, M., Pece, A., Cornoldi, C., Pietrini, P., 2006. Why Cyclops could not compete with Ulysses: monocular vision and mental images. NeuroReport 17, 723-726]. The aim of the present study was to assess whether the onset timing of a severe (but not total) sight loss may influence spatial imagery abilities based on haptic input. To this purpose, a group of late severe visually impaired people and a matched group of normally sighted participants (all blindfolded) were presented with an imagery task requiring to memorize and retrieve a number of locations presented on tactile matrices. Results indicate that a severe visual deficit occurring later in life significantly impairs spatial imagery abilities to a greater extent than in the case of congenital blindness, probably as a consequence of a modest development of specific compensatory mechanisms associated with congenital deficits.

Why Cyclops could not compete with Ulysses: monocular vision and mental images.

The present research demonstrates that the limitations of congenitally blind people in tasks requiring the processing of mental images are specifically related to the absence of binocular vision and not to the absence of vision per se. We contrasted three different groups of participants: sighted; visually impaired, with reduced binocular vision; monocular, with a normal visual acuity although in one eye only. Visually impaired participants (i.e. blurred vision) show a pattern of performance comparable to that of the sighted. In contrast, monocular participants show a similar pattern of performance to congenitally blind individuals despite being able to see perfectly well. These results shed new light on the relationship between perception and imagery and on the characteristics of sequential and simultaneous processes in the human brain.