Using functional magnetic resonance imaging (fMRI), we mapped the retinotopic organization throughout the visual cortex of fixating monkeys. The retinotopy observed in areas V1, V2, and V3 was completely consistent with the classical view. V1 and V3 were bordered rostrally by a vertical meridian representation, and V2 was bordered by a horizontal meridian. More anterior in occipital cortex, both areas V3A and MT-V5 had lower and upper visual field representations split by a horizontal meridian. The rostral border of dorsal V4 was characterized by the gradual transition of a representation of the vertical meridian (dorsally) to a representation of the horizontal meridian (more ventrally). Central and ventral V4, on the other hand, were rostrally bordered by a representation of the horizontal meridian. The eccentricity lines ran perpendicular to the ventral V3-V4 border but were parallel to the dorsal V3-V4 border. These results indicate different retinotopic organizations within dorsal and ventral V4, sugge...

The Bezold-Jarisch depressor reflex, implicated in myocardial ischemia and aortic stenosis, and possibly in shock sequences, elicits a profound fall in arterial pressure (AP), heart rate (HR) and apnea. The sites and patterning of central neural substrates involved in mediating this reflex remain unclear. Using functional magnetic resonance imaging procedures to examine brain activity, we elicited the Bezold-Jarish reflex via i.v. 5-hydroxytryptamine (5HT) in 9 isofluorane-anaesthetized adult cats (4.7T, TR=8 secs, TE=25 ms, FOV=8 cm, flip angle=90 degrees, voxel dimensions=0.625 x 0.625x2 mm). Intravenous 5HT (10-30mg/kg) evoked a rapid onset fall in AP (mean=20%), HR decline (mean=18%) and a prolonged apnea (mean=25secs). Signal intensity (SI) fell in brainstem cardiovascular regions (nucleus tractus solitarius, caudal and rostral ventrolateral medulla), and also in the caudal midline medulla, multiple regions of the cerebellum (deep nuclei, vermis) and the dorsolateral pons. In contrast, rostral brain s...

If attention is divided during learning, memory suffers. Nevertheless, individuals can learn information with divided attention. This event-related functional magnetic resonance imaging (fMRI) study ( n = 17) investigated what neural processes support (1) learning with divided attention and (2) retrieval of information learned with divided attention. Participants encoded words (Is the word abstract or concrete?) while performing an auditory discrimination task (press a button whenever an auditory pattern changes). The auditory task was easy or hard, depending on the similarity of the patterns. A behavioral study indicated that detailed (“recollective”) information was more likely to be present for words encoded with the easy versus the hard concurrent task. Words encoded with the hard versus the easy concurrent task, in contrast, were more likely to rely on less detailed (“familiarity”-based) information. fMRI revealed encoding-related activation in the left prefrontal cortex (PFC) and left hippocampus tha...

14C-labeled α-aminoisobutyric acid (AIB)-based quantitative autoradiography (QAR) was used to confirm MRI observations of loss of BBB integrity during reperfusion in a rat model of transient, unilateral, focal cerebral ischemia. All MRI observations were made using a 7-Tesla system. Diffusion- and T2-weighted imaging (DWI and T2WI, respectively) were performed during and after 3 hours of ischemia to identify the ischemic lesion. Qualitative and quantitative assessment of BBB integrity were done by serial scanning using T1-weighted imaging (T1WI) Look-Locker sequence to track a bolus injection of a gadolinium-chelate (Gd-DTPA). Immediately afterwards the rats were injected with a 14C-AIB bolus for QAR. The MRI images were processed to generate tissue segmentation maps and regions of interest (ROI) that demonstrated Gd-DTPA leakage. The ROI corresponded closely with regions showing 14C-AIB extravasation (i.e. BBB opening) on the autoradiograms. Transfer constants (Ki) were generated for the ROI from QAR data...

The human brain thalami play essential roles in integrating cognitive, sensory, and motor functions. In multiple sclerosis (MS), quantitative magnetic resonance imaging (qMRI) measurements of the thalami provide important biomarkers of disease progression, but late development and aging confound the interpretation of data collected from patients over a wide age range. Thalamic tissue volume loss due to natural aging and its interplay with lesion-driven pathology has not been investigated previously. In this work, we used standardized thalamic volumetry combined with diffusion tensor imaging, T2 relaxometry, and lesion mapping on large cohorts of controls ( N = 255, age range = 6.2–69.1 years) and MS patients ( N = 109, age range = 20.8–68.5 years) to demonstrate early age- and lesion-independent thalamic neurodegeneration.

Because environmental information is often suboptimal, visual perception must frequently rely on the brain's reconstruction of contours absent from retinal images. Illusory contour (IC) stimuli have been used to investigate these “filling-in” processes. Intracranial recordings and neuroimaging studies show IC sensitivity in lower-tier area V2, and to a lesser extent V1. Some interpret these data as evidence for feedforward processing of IC stimuli, beginning at lower-tier visual areas. On the basis of lesion, visual evoked potentials (VEP), and neuroimaging evidence, others contend that IC sensitivity is a later, higher-order process. Whether IC sensitivity seen in lower-tier areas indexes feedforward or feedback processing remains unresolved. In a series of experiments, we addressed the spatiotemporal dynamics of IC processing. Centrally presented IC stimuli resulted in early VEP modulation (88–100 msec) over lateral–occipital (LOC) scalp—the IC effect. The IC effect followed visual response onset by 40 m...

We have examined the activity levels produced in various areas of the human occipital cortex in response to various motion stimuli using functional magnetic resonance imaging (fMRI) methods. In addition to standard luminance-defined (first-order) motion, three types of second-order motion were used. The areas examined were the motion area V5 (MT) and the following areas that were delineated using retinotopic mapping procedures: V1, V2, V3, VP, V3A, and a new area that we refer to as V3B. Area V5 is strongly activated by second-order as well as by first-order motion. This activation is highly motion-specific. Areas V1 and V2 give good responses to all motion stimuli, but the activity seems to be related primarily to the local spatial and temporal structure in the image rather than to motion processing. Area V3 and its ventral counterpart VP also respond well to all our stimuli and show a slightly greater degree of motion specificity than do V1 and V2. Unlike V1 and V2, the response in V3 and VP is significa...

Prior knowledge of the probabilities concerning decision alternatives facilitates the selection of more likely alternatives to the disadvantage of others. The neural basis of prior probability (PP) integration into the decision-making process and associated preparatory processes is, however, still essentially unknown. Furthermore, trial-to-trial fluctuations in PP processing have not been considered thus far. In a previous study, we found that the amplitude of the contingent negative variation (CNV) in a precueing task is sensitive to PP information ([Scheibe et al., 2009][1]). We investigated brain regions with a parametric relationship between neural activity and PP and those regions involved in PP processing on a trial-to-trial basis in simultaneously recorded electroencephalographic (EEG) and functional magnetic resonance imaging (fMRI) data. Conventional fMRI analysis focusing on the information content of the probability precue revealed increasing activation of the posterior medial frontal cortex wit...

While ubiquitous, pharmacological manipulation of consciousness remains poorly defined and incompletely understood ([Prys-Roberts, 1987][1]). This retards anesthetic drug development, confounds interpretation of animal studies conducted under anesthesia, and limits the sensitivity of clinical monitors of cerebral function to intact perception. Animal and human studies propose a functional “switch” at the level of the thalamus, with inhibition of thalamo-cortical transmission characterizing loss of consciousness ([Alkire et al., 2000][2]; [Mashour, 2006][3]). We investigated the effects of propofol, widely used for anesthesia and sedation, on spontaneous and evoked cerebral activity using functional magnetic resonance imaging (fMRI). A series of auditory and noxious stimuli was presented to eight healthy volunteers at three behavioral states: awake, “sedated” and “unresponsive.” Performance in a verbal task and the absence of a response to verbal stimulation, rather than propofol concentrations, were used t...

Age is associated with substantial macrostructural brain changes. While some recent magnetic resonance imaging studies have reported larger age effects in men than women, others find no sex differences. As brain morphometry is a potentially important tool in diagnosis and monitoring of age-related neurological diseases, e.g., Alzheimer's disease (AD), it is important to know whether sex influences brain aging. We analyzed cross-sectional magnetic resonance scans from 1143 healthy participants from seven subsamples provided by four independent research groups. In addition, 96 patients with mild AD were included. Estimates of cortical thickness continuously across the brain surface, as well as volume of 17 subcortical structures, were obtained by use of automated segmentation tools (FreeSurfer). In the healthy participants, no differences in aging slopes between women and men were found in any part of the cortex. Pallidum corrected for intracranial volume showed slightly higher age correlations for men. The ...