Subcortical representation of non-Fourier image features.

A fundamental goal of visual neuroscience is to identify the neural pathways representing different image features. It is widely argued that the early stages of these pathways represent linear features of the visual scene and that the nonlinearities necessary to represent complex visual patterns are introduced later in cortex. We tested this by comparing the responses of subcortical and cortical neurons to interference patterns constructed by summing sinusoidal gratings. Although a linear mechanism can detect the component gratings, a nonlinear mechanism is required to detect an interference pattern resulting from their sum. Consistent with in vitro retinal ganglion cell recordings, we found that interference patterns are represented subcortically by cat LGN Y-cells, but not X-cells. Linear and nonlinear tuning properties of LGN Y-cells were then characterized and compared quantitatively with those of cortical area 18 neurons responsive to interference patterns. This comparison revealed a high degree of similarity between the two neural populations, including the following: (1) the representation of similar spatial frequencies in both their linear and nonlinear responses, (2) comparable orientation selectivity for the high spatial frequency carrier of interference patterns, and (3) the same difference in their temporal frequency selectivity for drifting gratings versus the envelope of interference patterns. The present findings demonstrate that the nonlinear subcortical Y-cell pathway represents complex visual patterns and likely underlies cortical responses to interference patterns. We suggest that linear and nonlinear mechanisms important for encoding visual scenes emerge in parallel through distinct pathways originating at the retina.

The organization of spatial frequency maps measured by cortical flavoprotein autofluorescence.

To determine the organization of spatial frequency (SF) preference within cat Area 17, we imaged responses to stimuli with different SFs using optical intrinsic signals (ISI) and flavoprotein autofluorescence (AFI). Previous studies have suggested that neurons cluster based on SF preference, but a recent report argued that SF maps measured with ISI were artifacts of the vascular bed. Because AFI derives from a non-hemodynamic signal, it is less contaminated by vasculature. The two independent imaging methods produced similar SF preference maps in the same animals, suggesting that the patchy organization of SF preference is a genuine feature of Area 17.

Models and measurements of functional maps in V1.

The organization of primary visual cortex has been heavily studied for nearly 50 years, and in the last 20 years functional imaging has provided high-resolution maps of its tangential organization. Recently, however, the usefulness of maps like those of orientation and spatial frequency (SF) preference has been called into question because they do not, by themselves, predict how moving images are represented in V1. In this review, we discuss a model for cortical responses (the spatiotemporal filtering model) that specifies the types of cortical maps needed to predict distributed activity within V1. We then review the structure and interrelationships of several of these maps, including those of orientation, SF, and temporal frequency preference. Finally, we discuss tests of the model and the sufficiency of the requisite maps in predicting distributed cortical responses. Although the spatiotemporal filtering model does not account for all responses within V1, it does, with reasonable accuracy, predict population responses to a variety of complex stimuli.

The representation of complex images in spatial frequency domains of primary visual cortex.

The organization of cat primary visual cortex has been well mapped using simple stimuli such as sinusoidal gratings, revealing superimposed maps of orientation and spatial frequency preferences. However, it is not yet understood how complex images are represented across these maps. In this study, we ask whether a linear filter model can explain how cortical spatial frequency domains are activated by complex images. The model assumes that the response to a stimulus at any point on the cortical surface can be predicted by its individual orientation, spatial frequency, and temporal frequency tuning curves. To test this model, we imaged the pattern of activity within cat area 17 in response to stimuli composed of multiple spatial frequencies. Consistent with the predictions of the model, the stimuli activated low and high spatial frequency domains differently: at low stimulus drift speeds, both domains were strongly activated, but activity fell off in high spatial frequency domains as drift speed increased. To determine whether the filter model quantitatively predicted the activity patterns, we measured the spatiotemporal tuning properties of the functional domains in vivo and calculated expected response amplitudes from the model. The model accurately predicted cortical response patterns for two types of complex stimuli drifting at a variety of speeds. These results suggest that the distributed activity of primary visual cortex can be predicted from cortical maps like those of orientation and SF preference generated using simple, sinusoidal stimuli, and that dynamic visual acuity is degraded at or before the level of area 17.

Functional imaging of primary visual cortex using flavoprotein autofluorescence.

Neuronal autofluorescence, which results from the oxidation of flavoproteins in the electron transport chain, has recently been used to map cortical responses to sensory stimuli. This approach could represent a substantial improvement over other optical imaging methods because it is a direct (i.e., nonhemodynamic) measure of neuronal metabolism. However, its application to functional imaging has been limited because strong responses have been reported only in rodents. In this study, we demonstrate that autofluorescence imaging (AFI) can be used to map the functional organization of primary visual cortex in both mouse and cat. In cat area 17, orientation preference maps generated by AFI had the classic pinwheel structure and matched those generated by intrinsic signal imaging in the same imaged field. The spatiotemporal profile of the autofluorescence signal had several advantages over intrinsic signal imaging, including spatially restricted fluorescence throughout its response duration, reduced susceptibility to vascular artifacts, an improved spatial response profile, and a faster time course. These results indicate that AFI is a robust and useful measure of large-scale cortical activity patterns in visual mammals.

[Clinical trial of pregnancy terminations in 353 patients where amenorrhea was present for less than 49 days by 600 mg of RU 486 (administered orally) and 500 mg of sulprostone (Nalador) administered intramuscularly]. / Etude clinique de 353 cas d'IVG de moins de 49 jours d'amenorrhee realisee par: 600 mg de RU 486 voie buccale + sulprostone 500 mg IM (Nalador).

PIP: 354 women seeking abortions were treated at a hospital in Paris between February-September 1988 with 600 mg of RU 486 taken orally in 1 dose and an injection of 500 mg sulprostone 48 hours later. The women all had amenorrhea of less than 49 days. 1/3 were 18-25 years old, 1/2 were 25-35, and 16% were over 35. 206 were nulliparas. 110 were married and the rest were separated, widowed, divorced, or single. Sulprostone was injected early in the morning in the hospital and the women were discharged after expulsion of the products of conception, which occurred usually 2 1/2 to 3 1/2 hours later. If expulsion did not occur, the woman returned in 3 days for a sonogram to confirm uterine vacuity. 13 of the 354 women had RU 486 only. 2 refused the sulprostone and underwent aspiration and 11 experienced spontaneous expulsions in the 48 hours following RU 486 administration. 338 of the women had spontaneous expulsions. 2 pregnancies were terminated but not expelled and aspiration was required. 285 of the women expelled in the hospital within 4 hours of sulprostone administration and the other 55 did so at home 6 or more hours later. RU 486 was very well tolerated. Secondary effects were more common with sulprostone but generally subsided within 3 hours. 70 patients required treatment for uterine pain after sulprostone administration. 150 complained of nausea but only 6 required treatment. 5 women required aspiration of curettage for hemorrhage but none required transfusion. In 3 cases the hemorrhages were due to histologically proven retention. 1 patient developed endometritis 3 days after expulsion and another, who had a history of extrauterine pregnancy, developed salpingitis 15 days after expulsion. Both patients were treated with antibiotics. The method appears to be safe and effective. Its major disadvantages are that it prolongs the amount of time required for abortion and it frequently causes pelvic pain. The responsibility of the patient is also increased.^ieng

[Progestogen contraception using chlormadinone acetate in women presenting high vascular risk. (A gynecoendocrine, metabolic and vascular study)].

PIP: 20 women with metabolic, vascular, or gynecoendocrinological contraindications to use of combined oral contraceptives (OCs) or norsteroid progestins participated in a 6-month study of chlormadinone acetate, a progestin derived from 17-OH progesterone known for its weak androgenic activity. 5 mg doses of chlormadinone acetate were administered on the morning and evening of the 6th to the 26th cycle day for 3 woman and on the 8th to the 26th cycle day for 17 others. Blood tests were conducted during the luteal phase after fasting. The average age of the study subjects was 29.9, the average weight was 57.8 kg, and the average height was 161 cm. There were no significant variations over the course of the study in weight, blood pressure, renin substrate, high density lipoprotein (HDL) cholesterol, triglycerides, plasma apo-B, or antithrombin III. There was a significant reduction in apoprotein A1, the principle protein fraction of high density lipoproteins, from the 3rd to the 6th cycles, and a nonsignificant reduction of the apoprotein B. The ratio of A1/B apoproteins was not significantly modified. There were no signs of hyperestrogenism, hyperandrogenic effects, or digestive intolerance. In most cases there was no significant change in cycle duration or intensity of menstrual bleeding. 3 patients were recurrently amenorrheic. The amount of bleeding was considered normal by 14 patients and diminished by 3. There were no cases of menorrhagia and 5 of minor metrorrhagia in the first 3 months of use. No pregnancies occurred. After voluntary termination of contraception, 2 patients rapidly became pregnant. Measurement of ovarian hormone levels and gonadotropins indicated that chlormadinone acetate at the prescribed dose completely inhibited progesterone secretion in all patients and considerably reduced the production of estradiol in the luteal phase. Chlormadinone acetate has the dual advantages of avoiding the estrogen-induced side effects of combined OCs and avoiding hyperestrogenism. The use of a progestin derived from 17-OH progesterone may offer a contraceptive method suitable for women with metabolic or vascular contraindications to combined OCs or gynecoendocrinological contraindications to low dose progestins, who are unable or unwilling to use mechanical or local contraceptives. Chlormadinone acetate should however remain a method for use under exceptional circumstances.^ieng