Induction field organization and simultaneous contrast

1991 ◽  
Author(s):  
Tiziano Agostini ◽  
Walter Gerbino
Keyword(s):  
Simultaneous Contrast ◽  
Induction Field ◽  
Field Organization

Comparison of the responses of AII amacrine cells in the dark- and light-adapted rabbit retina

1999 ◽  
Vol 16 (4) ◽  
pp. 653-665 ◽  
Author(s):  
DAIYAN XIN ◽  
STEWART A. BLOOMFIELD
Keyword(s):  
Receptive Field ◽  
Light Adaptation ◽  
Amacrine Cells ◽  
Bipolar Cells ◽  
Rabbit Retina ◽  
Response Component ◽  
Synaptic Inputs ◽  
Field Organization ◽  
Receptive Field Organization ◽  
Aii Amacrine Cells

We studied the light-evoked responses of AII amacrine cells in the rabbit retina under dark- and light-adapted conditions. In contrast to the results of previous studies, we found that AII cells display robust responses to light over a 6–7 log unit intensity range, well beyond the operating range of rod photoreceptors. Under dark adaptation, AII cells showed an ON-center/OFF-surround receptive-field organization. The intensity–response profile of the center-mediated response component followed a dual-limbed sigmoidal function indicating a transition from rod to cone mediation as stimulus intensities were increased. Following light adaptation, the receptive-field organization of AII cells changed dramatically. Light-adapted AII cells showed both ON- and OFF-responses to stimulation of the center receptive field, but we found no evidence for an antagonistic surround. Interestingly, the OFF-center response appeared first following rapid light adaptation and was then replaced gradually over a 1–4 min period by the emerging ON-center response component. Application of the metabotropic glutamate receptor agonist APB, the ionotropic glutamate blocker CNQX, 8-bromo-cGMP, and the nitric oxide donor SNAP all showed differential effects on the various center-mediated responses displayed by dark- and light-adapted AII cells. Taken together, these pharmacological results indicated that different synaptic circuits are responsible for the generation of the different AII cell responses. Specifically, the rod-driven ON-center responses are apparently derived from rod bipolar cell synaptic inputs, whereas the cone-driven ON-center responses arise from signals crossing the gap junctions between AII cells and ON-center cone bipolar cells. Additionally, the OFF-center response of light-adapted AII cells reflects direct synaptic inputs from OFF-center cone bipolar cells to AII dendritic processes in the distal inner plexiform layer.

scholarly journals Cognitive impairments from developmental exposure to serotonergic drugs: citalopram and MDMA

2013 ◽  
Vol 16 (6) ◽  
pp. 1383-1394 ◽  
Author(s):  
Tori L. Schaefer ◽  
Curtis E. Grace ◽  
Amanda A. Braun ◽  
Robyn M. Amos-Kroohs ◽  
Devon L. Graham ◽  
...  
Keyword(s):  
Brain Development ◽  
Cognitive Deficits ◽  
System Development ◽  
Third Trimester ◽  
Learning Deficits ◽  
Developmental Exposure ◽  
Target Field ◽  
Field Organization ◽  
Serotonergic Drugs

Abstract We previously showed that developmental 3,4-methylenedioxymethamphetamine (MDMA) treatment induces long-term spatial and egocentric learning and memory deficits and serotonin (5-HT) reductions. During brain development, 5-HT is a neurotrophic factor influencing neurogenesis, synaptogenesis, migration, and target field organization. MDMA (10 mg/kg × 4/d at 2 h intervals) given on post-natal day (PD) 11–20 in rats (a period of limbic system development that approximates human third trimester brain development) induces 50% reductions in 5-HT during treatment and 20% reductions when assessed as adults. To determine whether the 5-HT reduction is responsible for the cognitive deficits, we used citalopram (Cit) pretreatment to inhibit the effects of MDMA on 5-HT reuptake in a companion study. Cit attenuated MDMA-induced 5-HT reductions by 50% (Schaefer et al., 2012). Here we tested whether Cit (5 or 7.5 mg/kg × 2/d) pretreatment attenuates the cognitive effects of MDMA. Within each litter, different offspring were treated on PD11–20 with saline (Sal) + MDMA, Cit + MDMA, Cit + Sal or Sal + Sal. Neither spatial nor egocentric learning/memory was improved by Cit pretreatment. Unexpectedly, Cit + Sal (at both doses) produced spatial and egocentric learning deficits as severe as those caused by Sal + MDMA. These are the first data showing cognitive deficits resulting from developmental exposure to a selective serotonin reuptake inhibitor. These data indicate the need for further research on the long-term safety of antidepressants during pregnancy.

scholarly journals Two cases of trichromic vision

1905 ◽  
Vol 76 (508) ◽  
pp. 194-198
Keyword(s):  
Simultaneous Contrast ◽  
Greenish Yellow ◽  
Orange Yellow ◽  
Different Parts

1. One case (Professor J. J. Thomson) sees only three colours in the bright spectrum—red, green, and violet. He can distinguish nothing of the nature of pure yellow, like the sensation given him by the sodium flame in the spectrum. There is no definite colour to him at the portion of the spectrum where the normal sighted see pure blue. Reddish-green would describe the orange and yellow regions and greenish-violet the blue. λ 5950 (orange-yellow) is the point which differs most from red and green. There was no shortening of either end of the spectrum. The point of junction of the red and green differed somewhat in repeating the observations because of his great sensitiveness to simultaneous contrast. It was, however, always in the orange or orange-yellow, never in the yellow of the normal sighted. Difference of Hue Perception .—I then tested him with my apparatus for ascertaining the size of different parts of the spectrum which appear monochromatic, and found that he was defective in distinguishing differences of hue. A portion of the spectrum corresponding to the D lines, and isolated by two shutters in the eye-piece of the spectroscope, was first shown. The shutter on the red side was gradually opened until a difference of hue was seen. The monochromatic patch extended from λ 5889 to λ 6052, being exactly half as large again as that of the normal sighted, which occupies the space from λ 5889 to λ 5998. The monochromatic patch the called greenish-yellow. His monochromatic patch in the centre of the green bore exactly the same proportion to mine as in the case of the orange-yellow, being just half as large again.

Simplified Magnetic Induction Field of Magnetite Particles With Irregular Shape

2019 ◽  
Vol 55 (1) ◽  
pp. 1-5
Author(s):  
Jiangang Ku ◽  
Weixin Wu ◽  
Rongdong Deng ◽  
Weiran Zuo ◽  
Wanzhong Yin
Keyword(s):  
Magnetic Induction ◽  
Irregular Shape ◽  
Induction Field ◽  
Magnetic Induction Field ◽  
Magnetite Particles

Two-dimensional receptive-field organization in striate cortical neurons of the cat

1994 ◽  
Vol 11 (4) ◽  
pp. 703-720 ◽  
Author(s):  
Ming Sun ◽  
A. B. Bonds
Keyword(s):  
Receptive Field ◽  
Cortical Neurons ◽  
Ocular Dominance ◽  
Receptive Fields ◽  
Field Size ◽  
Two Dimensional ◽  
Cortical Layers ◽  
Field Organization ◽  
Receptive Field Organization ◽  
Cortical Receptive Fields

AbstractThe two-dimensional organization of receptive fields (RFs) of 44 cells in the cat visual cortex and four cells from the cat LGN was measured by stimulation with either dots or bars of light. The light bars were presented in different positions and orientations centered on the RFs. The RFs found were arbitrarily divided into four general types: Punctate, resembling DOG filters (11%); those resembling Gabor filters (9%); elongate (36%); and multipeaked-type (44%). Elongate RFs, usually found in simple cells, could show more than one excitatory band or bifurcation of excitatory regions. Although regions inhibitory to a given stimulus transition (e.g. ON) often coincided with regions excitatory to the opposite transition (e.g. OFF), this was by no means the rule. Measurements were highly repeatable and stable over periods of at least 1 h. A comparison between measurements made with dots and with bars showed reasonable matches in about 40% of the cases. In general, bar-based measurements revealed larger RFs with more structure, especially with respect to inhibitory regions. Inactivation of lower cortical layers (V-VI) by local GABA injection was found to reduce sharpness of detail and to increase both receptive-field size and noise in upper layer cells, suggesting vertically organized RF mechanisms. Across the population, some cells bore close resemblance to theoretically proposed filters, while others had a complexity that was clearly not generalizable, to the extent that they seemed more suited to detection of specific structures. We would speculate that the broadly varying forms of cat cortical receptive fields result from developmental processes akin to those that form ocular-dominance columns, but on a smaller scale.

Dynamic aspects of receptive field organization in area VI of the macaque monkey

1992 ◽  
pp. 177-188
Author(s):  
James M. Fox ◽  
David C. Van Essen ◽  
Tobias Delbrück ◽  
Jack Gallant ◽  
Charles H. Anderson
Keyword(s):  
Receptive Field ◽  
Macaque Monkey ◽  
Field Organization ◽  
Receptive Field Organization
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