Biomedical subjects
Publications and source records attributed to Andreas Kleinschmidt.
At the intersection of two intensely belabored fields, primary visual cortex (V1) function and neural mechanisms of cognitive control, Jack et al. (in this issue of Neuron) report a neural signal that is neither related to stimulus representation nor spatial attention. Instead, this endogenous signal correlates with task structure and raises new questions.
OBJECTIVE: The risk for conduct disorder (CD) is markedly increased in children with specific temperament dimensions. Here, we investigated whether adverse temperament factors might contribute to an impairment in neural mechanisms underlying the regulation of aggressive behaviour. METHOD: Functional magnetic resonance imaging was performed in 13 male adolescents with CD aged 9 to 14 years and in 14 healthy age and sex-matched control subjects at 1.5T. During scanning, subjects looked at pictures from the International Affective Picture System with neutral or strong negative emotional valence. Temperament was assessed using the German version of the Junior Temperament and Character Inventory. In addition, behavioural control strategies (Wisconsin Card Sorting, Four Pack Card Playing Task) and sociomoral reasoning (Sociomoral Reflection Measure Short Form) were tested to behaviourally characterise the study groups. RESULTS: When comparing CD patients with healthy controls, we found reduced activation in the right anterior cingulate cortex (ACC) in response to negative affective pictures. The temperament dimension 'novelty seeking' was a significant predictor for ACC responsiveness to affective pictures as revealed by a stepwise multiple regression analysis (beta=-0.53, p<0.01). Moreover, individuals with high 'novelty seeking' scores chose more disadvantageous strategies in the Four Pack Card Playing Task (p<0.05) and were characterised by a lower level of sociomoral reasoning (p<0.05). CONCLUSION: The results of this study provide a link between temperament factors and neural correlates of emotion processing in adolesecents with conduct disorder.
PURPOSE: To illustrate a functional interpretation of blood oxygen level-dependent (BOLD) signal changes associated with generalized spike-and-wave discharges in patients with absence seizures and to demonstrate the reproducibility of these findings in one case. METHODS: In a 47 year-old patient with frequent absence seizures, BOLD signal changes during generalized spike-and-wave discharges (GSWD) were mapped by using simultaneous and continuous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) at 1.5 T and 6 months later at 3 T. GSWDs were modeled as individual events and as blocks. RESULTS: The patient studied exhibited frequent generalized spike-wave activity with temporal properties ideal for study with EEG/fMRI. Highly reproducible GSWD-associated fMRI signal decreases (deactivations) were seen in bilateral frontal and temporoparietal cortices and the precuneus, in addition to activations in occipital cortex and, at 3 T, the posterior thalamus. CONCLUSIONS: The GSWD-associated changes seen here involve cortical regions that have been shown to be more active at conscious rest compared with sleep and with various types of extroverted perception and action. These regions have been proposed to constitute the core of a functional "default mode" system. We propose that the findings of deactivation of this distributed brain system during GSWDs mirrors the clinical manifestation of GSWDs (i.e., absence seizures). Furthermore, we suggest that these deactivations may reflect the functional consequences of GSWDs on physiologic brain activity at rest rather than direct hemodynamic correlates of epileptic discharges.
Recognizing the voices of people we know does not only activate "voice areas" in the temporal lobe but also extraauditory areas including the fusiform "face area" (FFA). This cross-modal effect could reflect that individual face and voice information become specifically associated when becoming acquainted with a person. Here, we addressed whether the ability to have individual face representations 1) plays a role in voice recognition and 2) is required to observe cross-modal responses to voices in face areas. We compared speaker recognition performance and neuroimaging responses during the processing of familiar and nonfamiliar speakers' voices in a developmental prosopagnosic subject (SO) with the respective findings obtained in a group of 9 control subjects. Despite scoring worse than controls on recognition of familiar speakers' voices, SO had normal cross-modal responses in the FFA and normal connectivity between FFA and the voice regions. However, she had reduced activations in areas that usually respond to familiarity with people. An indication for the malfunctioning of her FFA was reduced connectivity of the FFA to a subset of these supramodal areas. In combination these data suggest that 1) voice recognition benefits from the ability to process faces at an individual level and 2) cross-modal association of voices and faces in the brain is achieved by a sensory binding and does not depend on a top-down mechanism subsequent to successful person recognition.
Pioneering mapping studies of the human cortex have established the notion of somatotopy in sensory representation, which transpired into Penfield and Rasmussen's famous sensory homunculus diagram. However, regarding the primary cortical representation of the genitals, classical and modern findings appear to be at odds with the principle of somatotopy, often assigning it to the cortex on the mesial wall. Using functional neuroimaging, we established a mediolateral sequence of somatosensory foot, penis, and lower abdominal wall representation on the contralateral postcentral gyrus in primary sensory cortex and a bilateral secondary somatosensory representation in the parietal operculum.
BACKGROUND: It is widely held that aggression and antisocial behavior arise as a consequence of a deficiency in responding to emotional cues in the social environment. We asked whether neural responses evoked by affect-laden pictures would be abnormal in adolescents with conduct disorder (CD). METHODS: Functional magnetic resonance imaging during passive viewing of pictures with neutral or strong negative affective valence was performed in 13 male adolescents with severe CD aged 9 to 15 years and in 14 healthy age-matched control subjects. RESULTS: Main effects for negative-neutral affective valence included activations in the amygdala and hippocampus, ventral extrastriate visual cortex, and intraparietal sulcus bilaterally. There was a significant group-by-condition interaction in the right dorsal anterior cingulate cortex that was due to a pronounced deactivation in the patient group during viewing of negative pictures. When correcting for anxiety and depressive symptoms, we additionally found a reduced responsiveness of the left amygdala to negative pictures in patients compared with control subjects. CONCLUSIONS: We suggest that these findings reflect an impairment of both the recognition of emotional stimuli and the cognitive control of emotional behavior in patients with CD, resulting in a propensity for aggressive behavior.
The 'correspondence problem' refers to the ambiguity of apparent motion (AM) paths if several similar objects are displaced across successive displays. We investigated the effect of intrinsic object properties such as colour and luminance on AM paths, and used functional magnetic resonance imaging to localize neural correlates of correspondence matching in visual cortical regions. Human subjects looked at an AM display where two dots in diagonally opposite corners of an implicit rectangle were flashed in alternation with two dots in the other two corners, yielding spontaneous alternations between horizontal and vertical AM. The dots differed in colour or luminance, or were identical. Neural activity was analysed as a function of whether the perceived AM path matched the dots' colour or luminance, and was also compared to activity during bistable AM displays without correspondence cues. When AM paths matched colour and luminance cues, activity in early visual cortex was the same as during perception of uncued displays, whereas it was suppressed when perceived AM paths violated colour or luminance cues. Colour-sensitive extrastriate cortex (V4 complex) transiently activated whenever AM perception switched from a pattern violating colour correspondence to one consistent with colour. We propose that the neural correlate of correspondence in early visual cortex reflects regulatory mechanisms that flexibly gate early visual feature processing in accord with an overriding perceptual decision. Conversely, activation of feature-selective extrastriate regions depends on the type of cue used for correspondence matching and may reflect the salience of percepts that match in colour and motion.
Face and voice processing contribute to person recognition, but it remains unclear how the segregated specialized cortical modules interact. Using functional neuroimaging, we observed cross-modal responses to voices of familiar persons in the fusiform face area, as localized separately using visual stimuli. Voices of familiar persons only activated the face area during a task that emphasized speaker recognition over recognition of verbal content. Analyses of functional connectivity between cortical territories show that the fusiform face region is coupled with the superior temporal sulcus voice region during familiar speaker recognition, but not with any of the other cortical regions normally active in person recognition or in other tasks involving voices. These findings are relevant for models of the cognitive processes and neural circuitry involved in speaker recognition. They reveal that in the context of speaker recognition, the assessment of person familiarity does not necessarily engage supramodal cortical substrates but can result from the direct sharing of information between auditory voice and visual face regions.
We assessed the interference by distracter letters on target discrimination as a function of the distance between incompatible distracters and target. The slope of the response time-distance function supports a Mexican hat pattern of attentional modulation in the visual field. We relate the results to our recent finding of neural activity suppression in primary visual cortex coding locations in the vicinity of an attended region [Muller, N. G., & Kleinschmidt, A. (2004). The attentional 'spotlight's' penumbra: Center-surround modulation in striate cortex. Neuroreport, 15(6), 977-980]. As behavioral performance parallels activity modulation of primary visual cortex but not other areas we propose that perceptual capacities are determined by attentional response properties of V1.
By enhancing neural activity in respective retinotopic cortical representations attention increases the efficiency with which visual information at a selected location is processed. Behavioral data also suggest that information from the vicinity of the attended region is actively suppressed. In search for a physiological correlate of this 'spotlight's penumbra' we assessed neural responses in retinotopic representations of an attended location and of locations at different distances to it. Relative to passive viewing we found suppressed striate activity for the nearby but not for the far locations. This attention-driven center-surround distribution of neural activity may enhance the contrast between attended and non-attended objects. We relate the different behavior of extrastriate areas to their lower spatial resolution, i.e. larger receptive fields.
Is there a neural system dedicated to generic magnitude judgments? In this issue of Neuron, Pinel et al. report qualitative spatial overlap of fMRI responses during judgments of luminance, size, and numerical magnitude but also quantitative response differences in intraparietal cortex that mirror behavioral interference between perceptual and symbolic magnitude.
Several functional neuroimaging studies have observed response adaptation in face-sensitive regions when repeating identical face stimuli. To address whether this was due to low-level stimulus properties or facial identity, we decomposed pictures of faces into pictures preserving only the lower or higher parts of the normal frequency spectrum. In an event-related functional neuroimaging study, pairs of such pictures were sequentially presented that showed the same or different persons in the same or different frequency bands. This factorial design allowed to separate effects related to repetition of personal identity from those related to identical stimulus properties. In a random effects group analysis, activation in the right fusiform region was affected by repetition of personal identity regardless of changing or constant spatial scale. Responses in the more medial and posterior fusiform and lingual regions adapted with repetition of the same frequency band. An analysis in regions of interest determined individually as face responsive showed that repetition decreases for the same faces in fusiform face-responsive regions generalized across spatial frequency bands. Our results therefore point to a role of this area in discriminating individual faces at a level of representation that is invariant to changes in low-level stimulus properties, as spatial scale. The same invariance could not be detected in more posterior occipital face-responsive regions.
We recently found that in bistable apparent motion (AM) both the motion complex (hMT/V5+) and kinetic occipital area (KO) transiently activated whenever perception switched in the spinning wheel illusion. Here, we tested the specificity of this result with another bistable AM stimulus, the dynamic dot quartet, that does not involve kinetic contours. We observed significant activations in hMT/V5+, but not in KO. This indicates that neural activity in functionally specialized extrastriate visual areas during switching perception of ambiguous input depends on stimulus features in a finely tuned way suitable to encode perceptual content in the absence of sensory input changes.
We investigated the interaction between object- and space-based attention by measuring activity in early visual cortex. After central cueing, when subjects directed attention to a spatially defined part of an object, activity in early visual areas was enhanced at corresponding retinotopic representations but also at representations of other locations covered by the object. Different from the assumption of automatic attentional "spreading" within an object, however, activity was greater for representations of cued than of uncued locations on the same object. These findings support an interaction of object-based spatial selection with object-independent spatial mechanisms in directing attention. When the target stimulus did not appear at the expected location, we found higher activation in areas representing other locations on the same object than equidistant locations on other objects. Objects, hence, also guide spatial search, and this may account for the behaviorally observed delay in processing parts of an unattended object.
The triple-code theory of numerical processing postulates an abstract-semantic "number sense." Neuropsychology points to intraparietal cortex as a potential substrate, but previous functional neuroimaging studies did not dissociate the representation of numerical magnitude from task-driven effects on intraparietal activation. In an event-related fMRI study, we presented numbers, letters, and colors in the visual and auditory modality, asking subjects to respond to target items within each category. In the absence of explicit magnitude processing, numbers compared with letters and colors across modalities activated a bilateral region in the horizontal intraparietal sulcus. This stimulus-driven number-specific intraparietal response supports the idea of a supramodal number representation that is automatically accessed by presentation of numbers and may code magnitude information.
We studied with functional neuroimaging the cortical response to auditory sentences, comparing two recognition tasks that either targeted the speaker's voice or the verbal content. The right anterior superior temporal sulcus responded during the voice but not during the verbal content task. This response was therefore specifically related to the analysis of nonverbal features of speech. However, the dissociation between verbal and nonverbal analysis was only partial. Left middle temporal regions previously implicated in semantic processing responded in both tasks. This indicates that implicit semantic processing occurred even when the task directed attention to nonverbal input analysis. The verbal task yielded greater bilateral activation in the fusiform/lingual region, presumably reflecting an implicit translation of auditory sentences into visual representations. This result confirms the participation of visual cortical regions in verbal analysis of speech.
Visual conjunction search is proposed to be a multicomponent process which involves scaling and successive shifts of attention in space as well as object identification. Here, we first mapped brain areas sustaining the proposed attentional subprocesses and then tested whether their activity was modulated by search load, i.e., the number of shifts, as predicted by serial search models. Search load was manipulated indirectly by precueing a varying number of locations at which relevant objects were shown. Multiple subregions within the intraparietal sulcus (IPS) and the prefrontal cortex were activated after cueing. Activity in the right posterior IPS was modulated by the distance of attention shifts and in the left posterior IPS by "zooming out" to cover a large region of the visual field. More anterior subregions of the left IPS responded to object identification irrespective of the need for serial scanning. Corresponding regions in the right IPS were modulated parametrically with respect to search load, along with the right temporoparietal junction. These results support a functional segregation of subregions of the IPS. The posterior regions participate in large-scale shifts and scaling of the attentional focus and the anterior regions in object identification and rapid serial shifts during search. The sustained activation in the frontal eye fields after cueing suggests a role in maintaining attention in the periphery. Together with the findings in early visual areas from this experiment (Müller et al., 2003) the current observations are best accounted for by hybrid models of visual conjunction search, where parallel processing in visual and temporoparietal regions and serial scanning controlled by the right IPS cooperate.
In a previous functional neuroimaging study we found that early visual areas deactivated when a rotating optical flow stimulus elicited the illusion of self-motion (vection) compared with when it was perceived as a moving object. Here, we investigated whether electrical cortical responses to an independent central visual probe stimulus change as a function of whether optical flow stimulation in the periphery induces the illusion of self-motion or not. Visual-evoked potentials (VEPs) were obtained in response to pattern-reversals in the central visual field in the presence of a constant peripheral large-field optokinetic stimulus that rotated around the naso-occipital axis and induced intermittent sensations of vection. As control, VEPs were also recorded during a stationary peripheral stimulus and showed no difference than those obtained during optokinetic stimulation. The VEPs during constant peripheral stimulation were then divided into two groups according to the time spans where the subjects reported object- or self-motion, respectively. The N70 VEP component showed a significant amplitude reduction when, due to the peripheral stimulus, subjects experienced self-motion compared to when the peripheral stimulus was perceived as object-motion. This finding supplements and corroborates our recent evidence from functional neuroimaging that early visual cortex deactivates when a visual flow stimulus elicits the illusion of self-motion compared with when the same sensory input is interpreted as object-motion. This dampened responsiveness might reflect a redistribution of sensorial and attentional resources when the monitoring of self-motion relies on a sustained and veridical processing of optic flow and may be compromised by other sources of visual input.