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Mapping the Brain for Math. Reversible inactivation by direct cortical electrostimulation and transcranial magnetic stimulation.
No full textBrain laterality of numbers and calculation: Complex networks and their development
No full text: This chapter reviews notions about the lateralization of numbers and calculation in the brain, including its developmental pattern. Such notions have changed dramatically in recent decades. What was once considered a function almost exclusively located in the left hemisphere has been found to be sustained by complex brain networks encompassing both hemispheres. Depending on the specific task, however, each hemisphere has its own role. Much of this progress was determined by the convergency of investigations conducted with different methods. Contrary to traditional wisdom, the right hemisphere is not involved in arithmetic just as far as generic spatial aspects are concerned. Very specific arithmetic functions like remembering the spatial templates for complex operations, or processing of zero in complex numbers, are indeed sustained in specific right-sided areas. The system used in the typical adult appears to be the result of a complex pattern of development. The numerical brain clearly evolved from less mature to more advanced brain networks because of growth and education. Children seem to be equipped with the ability to represent the number nonverbally from a very early age. The bilateral processing of number-related tasks is however a late acquisition
Behavioural and neurophysiological evidence of semantic interaction between iconic gestures and words
No full textWe report two experiments that provide converging behavioural and neurophysiological evidence on the relationship between the meaning of iconic gestures and words. Experiment 1 exploited a semantic priming paradigm and revealed interference between gestures and words when they were not related in meaning, but no facilitation when they were. This result was confirmed in Experiment 2, where ERPs were recorded during silent word reading with the same paradigm. The analysis showed a negative deflection peaking near 400 ms (N400) and, in the left hemisphere, greater negative values for verbs than for nouns. Differently from the classical distribution obtained with verbal stimuli, we found an N400 that spread more over central-anterior areas of the scalp, suggesting that the meaning systems of gesture and language do not overlap completely. These results are consistent with the view that the meaning systems for gesture and speech are tightly integrated
Tracking the sensory and cognitive processes of shifts of spatial attention induced by numbers: an ERPs study
No full textThe relationship between space and number has become a focus of intensive investigation (Hubbard et al., 2005; Walsh, 2003). The present paper aims to explore the nature of attentional shifts induced by the perception of irrelevant numbers as it was shown by Fischer et al. (2003). We measured the event related potentials induced by the perception of visual lateralized targets cued by numbers that differed in their magnitude. Congruent trials were defined as those where a target presented in the Right Visual Field (RVF) followed a large number and those where a target presented in the Left Visual Field (LVF) followed a small number. Numbers generate a modulation of evoked potentials on targets as soon as 80 msec after the presentation of the target: congruency of the target determined the amplitude on perceptual P100 and cognitive P300 in both sides of presentation of the target. Although a typical distribution of the components was found, effects of congruency were distributed around anterior and Centro-Parietal sites. Due to the functional properties of the mentioned components, the present data suggest that, in fact, perception of numbers does affect the location of attention to external space. Moreover, the distribution of the congruency effect signals so that the representational nature of numbers makes a difference with respect to the stimuli classically used in cueing studies of visual attention to location. The role of top-down control generated by numbers is discussed
Numbers in the blind's eye
No full textBACKGROUND: Although lacking visual experience with numerosities, recent evidence shows that the blind perform similarly to sighted persons on numerical comparison or parity judgement tasks. In particular, on tasks presented in the auditory modality, the blind surprisingly show the same effect that appears in sighted persons, demonstrating that numbers are represented through a spatial code, i.e. the Spatial-Numerical Association of Response Codes (SNARC) effect. But, if this is the case, how is this numerical spatial representation processed in the brain of the blind?
PRINCIPAL FINDINGS: Here we report that, although blind and sighted people have similarly organized numerical representations, the attentional shifts generated by numbers have different electrophysiological correlates (sensorial N100 in the sighted and cognitive P300 in the blind).
CONCLUSIONS: These results highlight possible differences in the use of spatial representations acquired through modalities other than vision in the blind population
Electophysiological evidence of cross-modal priming between the meaning system of gesture and language
No full textBehavioral results showed an interference effect between the meaning of iconic gestures and that of unrelated words. ERPs analyses showed a greater P200 component for nouns than for verbs,
which was modulated by the relation with the preceding gesture,
and a clear N400 with greater negative values for verbs than for
nouns
Balancing the 2 Hemispheres in Simple Calculation: Evidence From Direct Cortical Electrostimulation
Get PDFHow do the parietal lobes contribute to simple calculation? Clinical and neuroimaging methods, which are based mainly on correlational evidence, have provided contrasting results so far. Here we used direct cortical electrostimulation during brain surgery to causally infer the role of the left and right parietal lobes in simple calculation. Stimulation provoked errors for addition and multiplication in different parietal areas on both hemispheres. Crucially, an innovative qualitative error analysis unveiled the functional contrast of the 2 parietal lobes. Right or left stimulation led to different types of substitution errors in multiplication, unveiling the function of the more active hemisphere. While inhibition of the left hemisphere led mainly to approximation errors, right hemisphere inhibition enhanced retrieval within a stored repertory. These results highlight the respective roles of each hemisphere in the network: rote retrieval of possible solutions by the left parietal areas and approximation to the correct solution by the right hemisphere. The bilateral orchestration between these functions guarantees precise calculation
Motion on numbers: Transcranial Magnetic Stimulation on VIPS alters both numerical and motion processes.
No full textIt has often been proposed that there is a close link between representation of number and space. In the present work, single-pulse transcranial magnetic stimulation (TMS) was applied to the ventral intraparietal sulcus (VIPS) to determine effects on performance in motion detection and number comparison tasks. Participants' reaction times and thresholds for perception of laterally presented coherent motion in random dot kinematograms increased significantly when the contralateral VIPS was stimulated in contrast to the interhemispheric sulcus (Experiment 1) and to the ipsilateral VIPS (Experiment 2). In number comparison tasks, participants compared the magnitude of the laterally presented numbers 1-9 with the number 5. Again, reaction times significantly increased when TMS was applied to the contralateral VIPS in contrast to control sites. The finding that VIPS-directed TMS results in impaired efficiency in both motion perception and number comparison suggests that these processes share a common neural substrate
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