Alberto Zani

The cognitive electrophysiology of mind and brain

Publisher Summary The event-related potentials (ERPs) of the brain are wave forms reflecting brain voltage fluctuations in time. This chapter highlights cognitive electrophysiology as a well-established field of science. The main assumption of cognitively oriented electrophysiological research is that cognition is implemented in the brain through physiological changes. Traditionally, for more than 100 years, cognitive and neurophysiological processes in humans have been studied by psychophysical and behavioral methods. The difficulty in differentiating cognition from brain localization is not, however, unique to neuroimaging and electrophysiological studies.

Electrophysiological evidence of a perceptual precedence of global vs. local visual information

Aim of the present study was to investigate the mechanisms of attentional selection of hierarchically organized visual patterns (compound letter stimuli), while subjects were engaged in target selection at either the global or local level. Event-related brain potentials (ERPs) were recorded using a high density electrode montage. Reaction times (RTs) to target stimuli were also recorded. RT data indicated the interference effect of global incongruent information with the local one. ERP data were consistent with behavioral data. In fact, the early sensory N115 component recorded at the primary visual areas exhibited smaller responses to locally attended elements when the global configuration was incongruent rather than congruent, suggesting an interference effect of the global with the local level. Conversely, no interference effect was found for globally attended configurations. These results strongly support the view of a perceptual advantage of globally conveyed information, very likely mediated by low spatial frequency channels. At later processing levels, N1 and P3 components were faster and larger when attention was paid to the global configuration. The difference between target and nontarget responses, indexing the attentional target selection, yielded a broad occipital-temporal negativity focused onto the left hemisphere in the attend-local, and over the right hemisphere in the attend-global condition. The present findings indicate a hemispheric asymmetry in cerebral activation during local/global processing. In addition, they provide robust evidence of a sensory precedence of global information.

From Orthography to Phonetics: ERP Measures of Grapheme-to-Phoneme Conversion Mechanisms in Reading

Neuroimaging has provided evidence that the first stages of visual word recognition activate a visual word-form center localized in the left extrastriate cortex (fusiform gyrus). Accordingly, neurological cases of patients suffering from pure alexia reported the left posterior occipital lobe as the possible locus of orthographic analysis. There is less agreement in the literature about which brain structures are involved in the subsequent stages of word processing and, in particular, their time course of activation. Functional magnetic resonance imaging and magnetic source imaging studies recently reported data that could indicate a dual route model of reading. These findings are particularly relevant to studies on the functional deficits associated with phonological and surface dyslexia. There is evidence for the existence of two different brain mechanisms supporting phonological processing in visual word recognition: one mechanism subserving assembled phonology for reading letter strings and another one subserving addressed phonology for reading meaningful words. However, available knowledge on the time course and neural locus of grapheme-to-phoneme conversion mechanisms in reading is still inadequate. In this study, we compared processing of meaningful and meaningless Italian words in a task requiring a phonemic/phonetic decision task. Stimuli were 1152 different orthographic stimuli presented in the central visual field. Half the stimuli were Italian words (with a high or low frequency of occurrence), the other half were meaningless strings of letters (legal pseudowords and letter strings). Event-related potentials were recorded from 28 scalp sites in 10 Italian university students. The task consisted of deciding about the presence/absence of a given phone in the hypothetical enunciation of word read: for example, Is there a/k/in cheese?. Results showed that lexical frequency and orthographical regularity affected linguistic processing within 150 msec poststimulus. Indeed, the amplitude of a centroparietal P150 varied as a function of stimulus type, being larger in response to high-frequency words than to lowfrequency ones and to words and pseudowords than to letter strings. This component might index visual categorization processes and recognition of familiar objects, being highly sensitive to orthographic regularity and ill-formedness of words. The amplitude of the P150 was the same in response to well-formed meaningless and to meaningful words, when these latter had a low lexical frequency. This might indicate that highly familiar words are recognized as meaningful unitary visual objects at very early stages of processing, through a visual route to an orthographic input lexicon. Moreover, the amplitude of the negativity recorded between 250 and 350 msec showed an anteroposterior topographic dissociation for access to the phonemic representation of wellor ill-formed strings of characters. Brain responses were larger over the left occipito-temporal regions during reading of words and pseudowords and over the left frontal regions during reading of letter strings.

Sex differences in the brain response to affective scenes with or without humans

Recent findings have demonstrated that women might be more reactive than men to viewing painful stimuli (vicarious response to pain), and therefore more empathic [Han, S., Fan, Y., & Mao, L. (2008). Gender difference in empathy for pain: An electrophysiological investigation. Brain Research, 1196, 85-93]. We investigated whether the two sexes differed in their cerebral responses to affective pictures portraying humans in different positive or negative contexts compared to natural or urban scenarios. 440 IAPS slides were presented to 24 Italian students (12 women and 12 men). Half the pictures displayed humans while the remaining scenes lacked visible persons. ERPs were recorded from 128 electrodes and swLORETA (standardized weighted Low-Resolution Electromagnetic Tomography) source reconstruction was performed. Occipital P115 was greater in response to persons than to scenes and was affected by the emotional valence of the human pictures. This suggests that processing of biologically relevant stimuli is prioritized. Orbitofrontal N2 was greater in response to positive than negative human pictures in women but not in men, and not to scenes. A late positivity (LP) to suffering humans far exceeded the response to negative scenes in women but not in men. In both sexes, the contrast suffering-minus-happy humans revealed a difference in the activation of the occipito/temporal, right occipital (BA19), bilateral parahippocampal, left dorsal prefrontal cortex (DPFC) and left amygdala. However, increased right amygdala and right frontal area activities were observed only in women. The humans-minus-scenes contrast revealed a difference in the activation of the middle occipital gyrus (MOG) in men, and of the left inferior parietal (BA40), left superior temporal gyrus (STG, BA38) and right cingulate (BA31) in women (270-290 ms). These data indicate a sex-related difference in the brain response to humans, possibly supporting human empathy.

Language switching mechanisms in simultaneous interpreters: an ERP study

Recent event-related potential (ERP) and neuroimaging studies suggest that bilingual individuals are able to inhibit the processing of a non-target language while speaking or reading in another language. The neural mechanisms subserving code switching still remain matter of debate. The aim of the present study was to shed some light on the neurofunctional bases of such mechanisms. ERPs were recorded in native Italian simultaneous interpreters and monolingual controls during a semantic processing task in which the subjects had to evaluate the sensibleness of final words of incomplete sentences. All participants were strictly right-handed. Interpreters knew at least four languages (from four to eight) at a professional level, from among 11 European and Asian languages, and had an excellent command of English (L2). Four hundred short sentences were presented visually; half of them had an unexpected final word, producing a semantic incongruence. Sentences could be entirely in Italian or in English (unmixed); alternatively, the body of the sentence could be in English and the final word in Italian or vice versa (mixed). ERPs were time locked to the onset of the final word. Both reaction times (RTs) and electrophysiological data indicated a lesser degree of hemispheric lateralization for linguistic function during L2 rather than L1 processing in interpreters. The first effect of lexical switching and code switching was recorded in the time window between 140 and 200 ms at left anterior sites. At N400 level, ERPs were significantly larger to L2 than to L1 words only in the mixed and not in the unmixed condition. No effect of language was observed in the unmixed condition, thus suggesting that the difference in L1/L2 processing was not related to a difference in proficiency, but rather to a different functional organization of semantic integration systems due to the later age of acquisition of L2 compared to L1. Interpreters were faster at reading and comprehending sentences in English ending with an Italian word than vice versa (L2 --> L1 switch).

Gender and parental status affect the visual cortical response to infant facial expression

This study sought to determine the influence of gender and parental status on the brain potentials elicited by viewing infant facial expressions. We used ERP recording during a judgement task of infant happy/distressed expression to investigate if viewer gender or parental status affects the visual cortical response at various stages of perceptual processing. ERPs were recorded in 38 adults (male/female, parents/non-parents) during processing of infant facial expressions that varied in valence and intensity. All infants were unfamiliar to viewers. The lateral occipital P110 response was much larger in women than in men, regardless of facial expression, thus indicating a gender difference in early visual processing. The occipitotemporal N160 response provided the first evidence of discrimination of expressions of discomfort and distress and demonstrated a significant gender difference within the parent group, thus suggesting a strong interactive influence of genetic predisposition and parental status on the responsivity of visual brain areas. The N245 component exhibited complete coding of the intensity of facial expression, including positive expressions. At this processing stage the cerebral responses of female and male non-parents were significantly smaller than those of parents and insensitive to differences in the intensity of infant suffering. Smaller P300 amplitudes were elicited in mothers versus fathers, especially with infant expressions of suffering. No major group differences were observed in cerebral responses to happy or comfortable expressions. These findings suggest that mere familiarity with infant faces does not explain group differences.

Neural markers of a greater female responsiveness to social stimuli.

BackgroundThere is fMRI evidence that women are neurally predisposed to process infant laughter and crying. Other findings show that women might be more empathic and sensitive than men to emotional facial expressions. However, no gender difference in the brain responses to persons and unanimated scenes has hitherto been demonstrated.ResultsTwenty-four men and women viewed 220 images portraying persons or landscapes and ERPs were recorded from 128 sites. In women, but not in men, the N2 component (210–270) was much larger to persons than to scenes. swLORETA showed significant bilateral activation of FG (BA19/37) in both genders when viewing persons as opposed to scenes. Only women showed a source of activity in the STG and in the right MOG (extra-striate body area, EBA), and only men in the left parahippocampal area (PPA).ConclusionA significant gender difference was found in activation of the left and right STG (BA22) and the cingulate cortex for the subtractive condition women minus men, thus indicating that women might have a greater preference or interest for social stimuli (faces and persons).

Observation of Static Pictures of Dynamic Actions Enhances the Activity of Movement-Related Brain Areas

Background Physiological studies of perfectly still observers have shown interesting correlations between increasing effortfulness of observed actions and increases in heart and respiration rates. Not much is known about the cortical response induced by observing effortful actions. The aim of this study was to investigate the time course and neural correlates of perception of implied motion, by presenting 260 pictures of human actions differing in degrees of dynamism and muscular exertion. ERPs were recorded from 128 sites in young male and female adults engaged in a secondary perceptual task. Principal Findings Our results indicate that even when the stimulus shows no explicit motion, observation of static photographs of human actions with implied motion produces a clear increase in cortical activation, manifest in a long-lasting positivity (LP) between 350–600 ms that is much greater to dynamic than less dynamic actions, especially in men. A swLORETA linear inverse solution computed on the dynamic-minus-static difference wave in the time window 380–430 ms showed that a series of regions was activated, including the right V5/MT, left EBA, left STS (BA38), left premotor (BA6) and motor (BA4) areas, cingulate and IF cortex. Conclusions and Significance Overall, the data suggest that corresponding mirror neurons respond more strongly to implied dynamic than to less dynamic actions. The sex difference might be partially cultural and reflect a preference of young adult males for highly dynamic actions depicting intense muscular activity, or a sporty context.

Electrophysiological indexes of illusory contours perception in humans.

The present study investigated brain mechanisms underlying the perception of illusory contours, using recordings of event-related potentials of the brain (ERPs) in right-handed individuals. Forty different stimuli were presented randomly 1600 times in foveal vision; twenty of them produced the perception of illusory contours of a Kanizsa square, the remaining were obtained rotating outwards the inducers and they did not produce any illusory percept. Half of them had white inducers on a black background and vice versa; half of them were symmetrical and the other half asymmetrical. In lateral occipital areas illusory percepts produced larger evoked responses starting as early as 145 ms post-stimulus with the N1 peak. ERP data did not provide evidence of right-sided lateralisation of the processes underlying illusory contours formation at sensory level, as suggested by some neuroimaging and neuropsychological studies. The two cerebral hemispheres were differently activated while the subjective patterns formation progressed through neural processing stages. Indeed, brain response to illusory contours was more pronounced in the left occipital area at N2 component level (about 250 ms post-stimulus) and at right parietal sites at the latency of P300 component. Both background luminance and stimulus symmetry interacted with illusory boundaries formation. Present results confirm the hypothesis that the integration of contours arises at early stages of visual processing and highlight the primary role of edges continuity and boundary alignment in illusory contours perception.

The emergence of semantic categorization in early visual processing: ERP indices of animal vs. artifact recognition.

BackgroundNeuroimaging and neuropsychological literature show functional dissociations in brain activity during processing of stimuli belonging to different semantic categories (e.g., animals, tools, faces, places), but little information is available about the time course of object perceptual categorization. The aim of the study was to provide information about the timing of processing stimuli from different semantic domains, without using verbal or naming paradigms, in order to observe the emergence of non-linguistic conceptual knowledge in the ventral stream visual pathway. Event related potentials (ERPs) were recorded in 18 healthy right-handed individuals as they performed a perceptual categorization task on 672 pairs of images of animals and man-made objects (i.e., artifacts).ResultsBehavioral responses to animal stimuli were ~50 ms faster and more accurate than those to artifacts. At early processing stages (120–180 ms) the right occipital-temporal cortex was more activated in response to animals than to artifacts as indexed by posterior N1 response, while frontal/central N1 (130–160) showed the opposite pattern. In the next processing stage (200–260) the response was stronger to artifacts and usable items at anterior temporal sites. The P300 component was smaller, and the central/parietal N400 component was larger to artifacts than to animals.ConclusionThe effect of animal and artifact categorization emerged at ~150 ms over the right occipital-temporal area as a stronger response of the ventral stream to animate, homomorphic, entities with faces and legs. The larger frontal/central N1 and the subsequent temporal activation for inanimate objects might reflect the prevalence of a functional rather than perceptual representation of manipulable tools compared to animals. Late ERP effects might reflect semantic integration and cognitive updating processes. Overall, the data are compatible with a modality-specific semantic memory account, in which sensory and action-related semantic features are represented in modality-specific brain areas.