Cortical field maps across human sensory cortex.

Cortical processing pathways for sensory information in the mammalian brain tend to be organized into topographical representations that encode various fundamental sensory dimensions. Numerous laboratories have now shown how these representations are organized into numerous cortical field maps (CMFs) across visual and auditory cortex, with each CFM supporting a specialized computation or set of computations that underlie the associated perceptual behaviors. An individual CFM is defined by two orthogonal topographical gradients that reflect two essential aspects of feature space for that sense.

Visual Field Map Clusters in High-Order Visual Processing: Organization of V3A/V3B and a New Cloverleaf Cluster in the Posterior Superior Temporal Sulcus.

The cortical hierarchy of the human visual system has been shown to be organized around retinal spatial coordinates throughout much of low- and mid-level visual processing. These regions contain visual field maps (VFMs) that each follows the organization of the retina, with neighboring aspects of the visual field processed in neighboring cortical locations. On a larger, macrostructural scale, groups of such sensory cortical field maps (CFMs) in both the visual and auditory systems are organized into roughly circular cloverleaf clusters.

Maps of the Auditory Cortex.

One of the fundamental properties of the mammalian brain is that sensory regions of cortex are formed of multiple, functionally specialized cortical field maps (CFMs). Each CFM comprises two orthogonal topographical representations, reflecting two essential aspects of sensory space. In auditory cortex, auditory field maps (AFMs) are defined by the combination of tonotopic gradients, representing the spectral aspects of sound (i.

Biosynthesis of the Fluorinated Natural Product Nucleocidin in Streptomyces calvus Is Dependent on the bldA-Specified Leu-tRNA(UUA) Molecule.

Nucleocidin is one of the very few natural products known to contain fluorine. Mysteriously, the nucleocidin producer Streptomyces calvus ATCC 13382 has not been observed to synthesize the compound since its discovery in 1956. Here, we report that complementation of S.

fMRI of the rod scotoma elucidates cortical rod pathways and implications for lesion measurements.

Are silencing, ectopic shifts, and receptive field (RF) scaling in cortical scotoma projection zones (SPZs) the result of long-term reorganization (plasticity) or short-term adaptation? Electrophysiological studies of SPZs after retinal lesions in animal models remain controversial, because they are unable to conclusively answer this question because of limitations of the methodology. Here, we used functional MRI (fMRI) visual field mapping through population RF (pRF) modeling with moving bar stimuli under photopic and scotopic conditions to measure the effects of the rod scotoma in human early visual cortex. As a naturally occurring central scotoma, it has a large cortical representation, is free of traumatic lesion complications, is completely reversible, and has not reorganized under normal conditions (but can as seen in rod monochromats).

A lack of experience-dependent plasticity after more than a decade of recovered sight.

In 2000, monocular vision was restored to M. M., who had been blind between the ages of 3 and 46 years.

Paradoxical visuomotor adaptation to reversed visual input is predicted by BDNF Val66Met polymorphism.

Brain-derived neurotrophic factor (BDNF) is the most abundant neurotrophin in the brain, influencing neural development, plasticity, and repair (Chen et al., 2004; Thoenen, 1995). The BDNF gene contains a single-nucleotide polymorphism (SNP) called Val(66)Met.

Visual cortex in aging and Alzheimer's disease: changes in visual field maps and population receptive fields.

Although several studies have suggested that cortical alterations underlie such age-related visual deficits as decreased acuity, little is known about what changes actually occur in visual cortex during healthy aging. Two recent studies showed changes in primary visual cortex (V1) during normal aging; however, no studies have characterized the effects of aging on visual cortex beyond V1, important measurements both for understanding the aging process and for comparison to changes in age-related diseases. Similarly, there is almost no information about changes in visual cortex in Alzheimer's disease (AD), the most common form of dementia.

A dynamic, embodied paradigm to investigate the role of serotonin in decision-making.

Serotonin (5-HT) is a neuromodulator that has been attributed to cost assessment and harm aversion. In this review, we look at the role 5-HT plays in making decisions when subjects are faced with potential harmful or costly outcomes. We review approaches for examining the serotonergic system in decision-making.

Visual Working Memory in Human Cortex.

Visual working memory (VWM) is the ability to maintain visual information in a readily available and easily updated state. Converging evidence has revealed that VWM capacity is limited by the number of maintained objects, which is about 3 - 4 for the average human. Recent work suggests that VWM capacity is also limited by the resolution required to maintain objects, which is tied to the objects' inherent complexity.

Orthogonal acoustic dimensions define auditory field maps in human cortex.

The functional organization of human auditory cortex has not yet been characterized beyond a rudimentary level of detail. Here, we use functional MRI to measure the microstructure of orthogonal tonotopic and periodotopic gradients forming complete auditory field maps (AFMs) in human core and belt auditory cortex. These AFMs show clear homologies to subfields of auditory cortex identified in nonhuman primates and in human cytoarchitectural studies.

Effects of healthy aging on human primary visual cortex.

Aging often results in reduced visual acuity from changes in both the eye and neural circuits [1-4]. In normally aging subjects, primary visual cortex has been shown to have reduced responses to visual stimulation [5]. It is not known, however, to what extent aging affects visual field representations and population receptive sizes in human primary visual cortex.

Visual maps: To merge or not to merge.

A recent study of a child born with one cerebral hemisphere has revealed an extreme developmental reorganization of visual cortex. Self-organizing visual maps demonstrate a surprisingly flexible restructuring in response to cortical loss.

Visual field maps in human cortex.

Much of the visual cortex is organized into visual field maps: nearby neurons have receptive fields at nearby locations in the image. Mammalian species generally have multiple visual field maps with each species having similar, but not identical, maps. The introduction of functional magnetic resonance imaging made it possible to identify visual field maps in human cortex, including several near (1) medial occipital (V1,V2,V3), (2) lateral occipital (LO-1,LO-2, hMT+), (3) ventral occipital (hV4, VO-1, VO-2), (4) dorsal occipital (V3A, V3B), and (5) posterior parietal cortex (IPS-0 to IPS-4).

Visual field maps and stimulus selectivity in human ventral occipital cortex.

Human visual cortex is organized into distinct visual field maps whose locations and properties provide important information about visual computations. There are two conflicting models of the organization and computational role of ventral occipital visual field maps. We report new functional MRI measurements that test these models.

Visual field map clusters in human cortex.

We describe the location and general properties of nine human visual field maps. The cortical location of each map, as well as many examples of the eccentricity and angular representations within these maps, are shown in a series of images that summarize a large set of functional MRI data. The organization and properties of these maps are compared and contrasted with descriptions by other investigators.

Lack of long-term cortical reorganization after macaque retinal lesions.

Several aspects of cortical organization are thought to remain plastic into adulthood, allowing cortical sensorimotor maps to be modified continuously by experience. This dynamic nature of cortical circuitry is important for learning, as well as for repair after injury to the nervous system. Electrophysiology studies suggest that adult macaque primary visual cortex (V1) undergoes large-scale reorganization within a few months after retinal lesioning, but this issue has not been conclusively settled.

Functional organization of human occipital-callosal fiber tracts.

Diffusion tensor imaging (DTI) and fiber tracking (FT) were used to measure the occipital lobe fiber tracts connecting the two hemispheres in individual human subjects. These tracts are important for normal vision. Also, damage to portions of these tracts is associated with alexia.

Visual field representations and locations of visual areas V1/2/3 in human visual cortex.

The position, surface area and visual field representation of human visual areas V1, V2 and V3 were measured using fMRI in 7 subjects (14 hemispheres). Cortical visual field maps of the central 12 deg were measured using rotating wedge and expanding ring stimuli. The boundaries between areas were identified using an automated procedure to fit an atlas of the expected visual field map to the data.

Visual areas in macaque cortex measured using functional magnetic resonance imaging.

We describe the first systematic functional magnetic resonance imaging (fMRI) measurements of visual field maps in macaque visual cortex. The boundaries of visual areas V1, V2, V3, V3A, V4, MT/V5, and TEO/V4A were identified using stimuli that create traveling waves of activity in retinotopically organized areas of the visual cortex. Furthermore, these stimuli were used to measure the dimensions of the representations of the central 11 degrees in V1-V3, quantitative visual field eccentricity functions for V1-V3 and MT, and the distribution of foveal and peripheral signals within the occipital lobe.

Functional measurements of human ventral occipital cortex: retinotopy and colour.

Human colour vision originates in the cone photoreceptors, whose spatial density peaks in the fovea and declines rapidly into the periphery. For this reason, one expects to find a large representation of the cone-rich fovea in those cortical locations that support colour perception. Human occipital cortex contains several distinct foveal representations including at least two that extend onto the ventral surface: a region thought to be critical for colour vision.

Reorganization of human cortical maps caused by inherited photoreceptor abnormalities.

We describe a compelling demonstration of large-scale developmental reorganization in the human visual pathways. The developmental reorganization was observed in rod monochromats, a rare group of congenitally colorblind individuals who virtually lack cone photoreceptor function. Normal controls had a cortical region, spanning several square centimeters, that responded to signals initiated in the all-cone foveola but was inactive under rod viewing conditions; in rod monochromats this cortical region responded powerfully to rod-initiated signals.