Fabiana Patria

Wide-Field Retinotopy Defines Human Cortical Visual Area V6

The retinotopic organization of a newly identified visual area near the midline in the dorsalmost part of the human parieto-occipital sulcus was mapped using high-field functional magnetic resonance imaging, cortical surface-based analysis, and wide-field retinotopic stimulation. This area was found in all 34 subjects that were mapped. It represents the contralateral visual hemifield in both hemispheres of all subjects, with upper fields located anterior and medial to areas V2/V3, and lower fields medial and slightly anterior to areas V3/V3A. It contains a representation of the center of gaze distinct from V3A, a large representation of the visual periphery, and a mirror-image representation of the visual field. Based on similarity in position, visuotopic organization, and relationship with the neighboring extrastriate visual areas, we suggest it might be the human homolog of macaque area V6, and perhaps of area M (medial) or DM (dorsomedial) of New World primates.

Identification of the neural sources of the pattern-reversal VEP

This study aimed to characterize the neural generators of the early components of the visual-evoked potential (VEP) to pattern-reversal gratings. Multichannel scalp recordings of VEPs and dipole modeling techniques were combined with functional magnetic resonance imaging (fMRI) and retinotopic mapping in order to estimate the locations of the cortical sources giving rise to VEP components in the first 200 ms poststimulus. Dipole locations were seeded to visual cortical areas in which fMRI activations were elicited by the same stimuli. The results provide strong evidence that the first major component of the VEP elicited by a pattern-reversal stimulus (N75/P85) arises from surface-negative activity in the primary visual cortex (area V1). Subsequent waveform components could be accounted for by dipoles that were in close proximity to fMRI activations in the following cortical areas: P95 (area MT/V5), P125/N135 (area V1), N150 (transverse parietal sulcus, TPS), N160 (ventral occipital areas VP, V4v, and V4/V8), and N180 (dorsal occipital areas V3A/V7). These results provide a detailed spatiotemporal profile of the cortical origins of the pattern-reversal VEP, which should enhance its utility in both clinical and basic studies of visual-perceptual processing.

Spatiotemporal analysis of the cortical sources of the steady-state visual evoked potential

This study aimed to characterize the neural generators of the steady‐state visual evoked potential (SSVEP) to repetitive, 6 Hz pattern‐reversal stimulation. Multichannel scalp recordings of SSVEPs and dipole modeling techniques were combined with functional magnetic resonance imaging (fMRI) and retinotopic mapping in order to estimate the locations of the cortical sources giving rise to the SSVEP elicited by pattern reversal. The time‐varying SSVEP scalp topography indicated contributions from two major cortical sources, which were localized in the medial occipital and mid‐temporal regions of the contralateral hemisphere. Colocalization of dipole locations with fMRI activation sites indicated that these two major sources of the SSVEP were located in primary visual cortex (V1) and in the motion sensitive (MT/V5) areas, respectively. Minor contributions from mid‐occipital (V3A) and ventral occipital (V4/V8) areas were also considered. Comparison of SSVEP phase information with timing information collected in a previous transient VEP study (Di Russo et al. [ 2005 ] Neuroimage 24:874–886) suggested that the sequence of cortical activation is similar for steady‐state and transient stimulation. These results provide a detailed spatiotemporal profile of the cortical origins of the SSVEP, which should enhance its use as an efficient clinical tool for evaluating visual‐cortical dysfunction as well as an investigative probe of the cortical mechanisms of visual‐perceptual processing. Hum. Brain Mapp, 2007.

Human V6: The Medial Motion Area

Cortical-surface-based functional Magnetic Resonance Imaging mapping techniques and wide-field retinotopic stimulation were used to verify the presence of pattern motion sensitivity in human area V6. Area V6 is highly selective for coherently moving fields of dots, both at individual and group levels and even with a visual stimulus of standard size. This stimulus is a functional localizer for V6. The wide retinotopic stimuli used here also revealed a retinotopic map in the middle temporal cortex (area MT/V5) surrounded by several polar-angle maps that resemble the mosaic of small areas found around macaque MT/V5. Our results suggest that the MT complex (MT+) may be specialized for the analysis of motion signals, whereas area V6 may be more involved in distinguishing object and self-motion.

The appreciation of wine by sommeliers: a functional magnetic resonance study of sensory integration

We set out to investigate how the expertise of a sommelier is embodied in neural circuitry by comparing brain activity elicited by wine tasting with that found in naive drinkers of wine. We used fMRI to study 7 sommeliers and 7 age- and sex-matched control subjects to test the hypothesis that any difference in brain activity would reflect a learned ability to integrate information from gustatory and olfactory senses with past experience. A group analysis showed activation of a cerebral network involving the left insula and adjoining orbito-frontal cortex in sommeliers. Both these areas have been implicated in gustatory/olfactory integration in primates. In addition, activation was found bilaterally in the dorsolateral prefrontal cortex, which is implicated in high-level cognitive processes such as working memory and selection of behavioral strategies. Naive individuals activated the primary gustatory cortex and brain areas, including the amygdala, implicated in emotional processing.

Intentional signals during saccadic and reaching delays in the human posterior parietal cortex

In the monkey posterior parietal cortex (PPC), there is clear evidence of anatomically segregated neuronal populations specialized for planning saccades and arm‐reaching movements. However, functional neuroimaging studies in humans have yielded controversial results. Here we show that the human PPC contains distinct subregions responsive to salient visual cues, some of which combine spatial and action‐related signals into ‘intentional’ signals. Participants underwent event‐related functional magnetic resonance imaging while performing delayed saccades and long‐range arm reaches instructed by visual cues. We focused on activity in the time period following the cue and preceding the actual movement. The use of individual cortical surface reconstructions with detailed sulcal labeling allowed the definition of six responsive regions with distinctive anatomical locations in the PPC. Each region exhibited a distinctive combination of transient and sustained signals during the delay, modulated by either the cue spatial location (contralateral vs. ipsilateral), the instructed action (saccades vs. reaching) or both. Importantly, a lateral and a medial dorsal parietal region showed sustained responses during the delay preferentially for contralateral saccadic and reaching trials, respectively. In the lateral region, preference for saccades was evident only as a more sustained response during saccadic vs. reaching delays, whereas the medial region also showed a higher transient response to cues signaling reaching vs. saccadic actions. These response profiles closely match the behavior of neurons in the macaque lateral and medial intraparietal area, respectively, and suggest that these corresponding human regions are encoding spatially directed action plans or ‘intentions’.

The representation of segmental information: An fMRI investigation of the consonant-vowel distinction

Harvard University, Cambridge, MA, USAAvailable online 23 July 2004IntroductionRecent studies suggest that consonants and vowels are repre-sented separately in cognitive/neural space. Much of the evidencecomes from research on dysgraphia (for review, see Miceli & Cap-asso, submitted). In the first place, letter substitution errors preservethe consonant/vowel (CV) status of the target (e.g., cinema fi ciremaor cinoma, but not cintma). Second, there are reports of selectiveimpairment for consonants or vowels. Additional evidence comesfrom disorders of phonology, demonstrating the dissociability be-tween consonants and vowels (Caramazza, Chialant, Capasso, Mthe ISI was variable (mean 6.75 s). The experimental task consistedof four conditions in which the target letter could be a vowel inposition 2 or 4 (e.g., cinema) or a consonant in position 3 or 5 (e.g.,cinema). Behavioral measures (error rate and RT) were obtainedduring fMRI scanning. In the control task, subjects saw a squiggleand pressed a button, depending on the direction of an arrow shownon the screen. As a baseline measure, subjects fixated the blankscreen. Stimulus presentation and response recording were imple-mented with Psyscope software (Cohen et al., 1993) running on aPower Macintosh computer (Apple, Cupertino, CA). The experimen-tal, control, and filler conditions were randomised in an event-relatedfMRI design and administered in three scanning sessions lasting eachabout 9 min.Image acquisition and analysisMR data were obtained on a 1.5 T Siemens Vision MR-scannerusing a whole-head coil. Blood oxygenlevel dependent (BOLD) imageswere acquired with an echo-planar imaging sequence (TR = 3.5 s,TE = 40 ms, flip angle = 90 ) in the axial plane (40 slices, 64 · 64matrix, 3 mm isotropic voxel size). For each subject, a high-resolution(1 · 1 · 1 mm) T1-weighted image of the whole brain was also ac-quired (TR = 11.4 ms, TE = 4.4 ms, flip angle = 10 , 256 · 256 ma-trix, 220 coronal slices).Functional images were processed in Matlab, using SPM99(Wellcome Department of Cognitive Neurology, London, UK) and in-house software (BrainShow). Images were corrected for slice timingand head movement, and then normalised to Montreal NeurologicalInstitute (MNI) coordinates and spatially smoothed (FWHM =6 mm). Images were analysed using a two-stage random effect ap-proach (Friston, Holmes, & Worsley, 1999).ResultsCompared to rest, the experimental task resulted in extensive ac-tivation of both occipital and temporal–mesial cortices, and of thefrontal and parietal lobes and the motor cortex on the left. Table 1shows the regions activated during: 1, the consonant verification taskvs the control task (C vs SQG); 2, the vowel verification task vs thecontrol task (V vs SQG); and 3, the consonant verification task vs thevowel verification task (C vs V). For each anatomical label and foreach significant comparison, coordinates in MNI space and Brodmannareas (BA) (Talairach & Tournoux, 1988) are given for voxels repre-senting local maxima of activation.Brain and Language 91 (2004) 35–37www.elsevier.com/locate/b&l

Brain activation for selective attention and cognitive interference using the digit-Stroop paradigm

Cognitive interference can occur while processing multiple attributes of stimuli. The classic method to study cognitive interference is the color-word Stroop task (1). With this method, interference occurs when the semantic attribute of a stimulus is incongruent with its physical attribute. Semantic interference appears to consistently activate the anterior cingulate cortex (ACC) and right prefrontal cortex (PFC), while some studies have also shown parietal activation (2). In digit-Stroop tasks (3), participants attend either to physical or semantic stimulus attributes, and these attributes exhibit cross-interference. Use of digit-Stroop tasks should indicate whether similar brain networks become activated during semantic and physical interference when humans attend to the opposite attribute, thereby providing evidence of a generalized network for cognitive interference.

Sensitivity enhancement of BOLD contrast functional MRI by real-time multi-echo EPI

Averaging of functional MR images obtained at different echo times with single-shot, multi-echo EPI reduces image intensity fluctuations related to thermal noise (1). With this method, we found increased BOLD contrast sensitivity in visual cortex as compared to conventional EPI (1). Since thermal noise has an inverse relationship with voxel size and other noise sources become dominant with increasing voxel sizes, it is of interest to investigate the voxel size dependence of the sensitivity enhancement. The current work extends prior findings by examining sensitivity increases for equivalent and larger voxels sizes in motor cortical area< A further motivation of the work was to implement real-time weighted averaging using the expected echo time dependence of the BOLD-effect as a weighting function to further increase sensitivity (1).