Biomedical subjects

Anna Wang Roe

Publications and source records attributed to Anna Wang Roe.

6 recordsLinked to original sources

PubMed2005

Optical imaging of SI topography in anesthetized and awake squirrel monkeys.

Orderly topographic maps in the primary somatosensory cortex (SI) serve as an anchor for our understanding of somatosensory cortical organization. However, this view is mostly based on data collected in the anesthetized animal. Less is known about these topographies in the awake primate. Even less is known about the relative activations of different subdivisions of SI (areas 3a, 3b, 1, and 2). Toward the goal of understanding the functional activation of SI, we conducted intrinsic signal optical imaging of areas 3b and 1 in awake squirrel monkeys. Monkeys were imaged repeatedly for a period of >2 years in awake and anesthetized states in response to vibrotactile and electrocutaneous stimuli presented to individual fingerpads. During this period, we found stable somatotopic maps in both the anesthetized and awake states, consistent with electrophysiologically recorded maps in areas 3b and 1 in the anesthetized state. In the awake animal, signal sizes were larger, but variability was greater, leading to decreased signal-to-noise ratios. Topographic activations were larger (in both area and amplitude) in the awake animal, suggesting either a less precise topography and/or more complex integration. This brings into question the role of a precise topographic map during behavior. In addition, whereas in the anesthetized animal strongest imaging signals were obtained from area 3b, in the awake animal, area 1 activation dominated over that in area 3b. Differences in relative dominance of area 3b versus area 1 suggest that inter-areal interactions in the alert animal differ substantially from that in the anesthetized animal.

Anesthesia↗

PubMed2005

Cortical processing of a brightness illusion.

Several brightness illusions indicate that borders can affect the perception of surfaces dramatically. In the Cornsweet illusion, two equiluminant surfaces appear to be different in brightness because of the contrast border between them. Here, we report the existence of cells in monkey visual cortex that respond to such an "illusory" brightness. We find that luminance responsive cells are located in color-activated regions (cytochrome oxidase blobs and bridges) of primary visual cortex (V1), whereas Cornsweet responsive cells are found preferentially in the color-activated regions (thin stripes) of second visual area (V2). This colocalization of brightness and color processing within V1 and V2 suggests a segregation of contour and surface processing in early visual pathways and a hierarchy of brightness information processing from V1 to V2 in monkeys.

Animals↗

PubMed2005

Optical imaging of functional organization of V1 and V2 in marmoset visual cortex.

Using optical imaging of intrinsic cortical signals, we examined the functional organization of visual cortical areas V1 and V2 of the marmoset (Callithrix jacchus). Previous studies have reported that adult marmosets do not have ocular dominance columns (ODCs); however, recent studies have called this into question. Using optical imaging methods, we examined whether ODCs could be detected in adult marmosets. We found evidence for functional ODCs in some marmosets but not in others. The activation patterns, when present, were relatively weak and appeared as a mosaic of irregular bands or islands. Consistent with studies in other New World monkeys, these data suggest the presence of ODC variability within the marmoset population. Orientation maps in V1 revealed iso-orientation domains organized in semicontinuous bands oriented orthogonal to the V1/V2 border, a pattern unlike that in Macaque monkey. The presence of directional preference maps in V1 was also suggested. In V2, similar to V2 in Macaque monkeys, stripe-like regions of orientation selectivity overlay the pale cytochrome oxidase regions of V2; zones not selective for orientation overlay the cytochrome thin stripes. However, unlike Macaques, we did not observe clear evidence for orientation maps overlying thick cytochrome oxidase stripes. In sum, our data suggest that significant organizational differences exist between the organization of V1 and V2 in the marmoset and that of Old World primates. Implications for the establishment of functional ocular dominance columns, the coestablishment of multiple featural maps, and cortical magnification factors are discussed.

Animals↗

PubMed2004

Modality maps within primate somatosensory cortex.

The sensations of pressure, flutter, and vibration are psychophysically distinct tactile modalities produced by frequency-specific vibrotactile stimulation of different mechanoreceptors in the skin. The information coded by the different low-threshold mechanoreceptors are carried by anatomically and electrophysiologically distinct pathways that remain separate at least up to and including the input stage of primary somatosensory cortex (SI) in primates, area 3b. Little is known about the functional organization of tactile representation beyond that stage. By using intrinsic optical imaging methods to record from area 1, the second processing stage of SI, we present evidence that pressure, flutter, and vibratory stimuli activate spatially distinct cortical domains in area 1, further strengthening the foundation for modality-specific processing streams in SI. These modality domains exhibit an organization that is unlike the discontinuous modality maps in visual area V2 but more like the continuous visual orientation maps in V1. The results demonstrate that psychophysically distinct sensory modalities can have fundamentally different modes of cortical representation.

Animals↗

PubMed2002

A chamber and artificial dura method for long-term optical imaging in the monkey.

Optical imaging over extended periods of time in non-human primates presents serious challenges because the dura mater must be removed to expose the cortical surface. We present a novel nylon imaging chamber with a transparent artificial dura implant, which allows repeated, long-term optical recordings from the cortex. The cylinder of the chamber is inserted into a cranial trephination and held in place with a minimum of screws and acrylic cement. A round patch of artificial dura with a perpendicular wall protects the cortical surface and slows re-growth of dural tissue within the chamber. A cap, manufactured from the same material as the cylinder, is screwed into the chamber and seals it completely. Over a period of 1-4 months, the chamber required a minimum of maintenance and stayed infection-free without local antibiotic application. We repeatedly performed optical imaging in the same animal with the advantages of shortened preparation time. To permit precise alignment and comparison of maps obtained from different imaging sessions, we developed a program that calculated a 2-dimensional spatial transformation between maps of different magnifications, translations, and distortions. We suggest that these methods provide a practical solution to long-term optical imaging in the anesthetized or alert monkey. The exclusive use of non-metallic materials offers the benefit of a lighter and more compact implant, and the possibility to perform MRI scans after chamber implantation.

Anesthesia↗

PubMed2002

Weakly modulated spike trains: significance, precision, and correction for sample size.

Many single-unit electrophysiological studies of visual cortex have investigated strong evoked responses to simple stimuli such as oriented gratings. Experiments involving other types of stimuli, such as natural scenes, higher-order features, and surface brightness, produce single-unit responses that are more difficult to interpret. Experiments with brightness, in particular, evoke single-unit responses that are typically weakly modulated. When the brightness is generated by a visual illusion such as the Cornsweet illusion, statistical tests are often necessary to distinguish true responses from baseline fluctuations. Here, using data collected from cat Areas 17 and 18 in response to real and illusory brightness stimuli, we provide a method for detecting and quantifying weak but significant periodic responses. By randomizing spike trains (via bootstrap methods), we provide confidence levels for response significance, permitting the evaluation of both weak and strong responses. We show that because of a strong dependence on total spike number, response significance can only be appropriately determined with randomized spike trains of similar spike number. Such randomizations can be performed for both stimulus-elicited and spontaneously occurring spike trains. By developing a method for generating randomized modulated spike trains (phase-restricted randomization) from actual recordings, we calculate upper and lower confidence limits of modulated spike trains and describe how measurement precision varies as a function of total spike count. Finally, using this randomization method, we describe how a correction function can be determined to correct for measurement bias introduced at low spike counts. These methods may also be useful in the study of small but potentially significant responses in other systems.

Action Potentials↗