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K Albus

Publications and source records attributed to K Albus.

At least 55 records · Page 3Linked to original sources
PubMed1980

Second and third visual areas of the cat: interindividual variability in retinotopic arrangement and cortical location.

1. The cortical location and the retinotopic arrangement of the second (V2) and third (V3) visual areas in the cat have been investigated with single and multiple unit recordings in anaesthetized and immobilized animals.2. V2 and V3 are arranged side by side anterior and medial to V1 and occupy the lateral gyrus and the postlateral sulcus. In addition, V2 spreads to postlateral parts of the lateral sulcus and, occasionally, to the posterior suprasylvian gyrus. The contralateral lower hemifield is represented on the lateral gyrus, the area centralis and the horizontal meridian are found in most animals in the anterior part of the postlateral sulcus, and the representation of the upper hemifield occupies the posterior part of the postlateral sulcus.3. The detailed retinotopic arrangement of the visual field maps shows two characteristic features. First, the retinotopy at the V2/V3 border differs between lower and upper hemifield. In the lower hemifield the periphery of the fields is represented, whereas in the upper hemifield the border between the representations is formed by a sector running along the horizontal meridian about 5-10 degrees in the upper hemifield. Thus the lower field arrangement resembles that of rodents, and the upper field arrangement is similar to that of primates. Secondly, the periphery of a part of the visual field is not continuously represented, but forms patches or islands (Donaldson & Whitteridge, 1977). The islands are bounded by visual field representations closer to the vertical meridian. The way the visual field is represented at the border between V2 and V3 introduces discontinuities into the visual field maps: adjacent parts of the visual field are not represented adjacently in these two prestriate areas.4. Cortical location and detailed retinotopic arrangement vary considerably from animal to animal, so that a representative map of V2 and V3 cannot be constructed. For example, the representation of the periphery of the horizontal meridian may be located either in the anterior portion of the postlateral sulcus or some mm more posteriorly, where the sulcus turns laterally. The representation of the area centralis in V3 is found either at the transition zone between lateral and postlateral sulcus, on the posterior suprasylvian gyrus, or in the posterior part of the postlateral sulcus.5. The entire hemifield is represented in V2 at least in some animals. In V3 the uppermost part of the vertical meridian seems not to be represented. In other animals only a restricted part of the contralateral visual field is represented in V2 or in V3. In these cases the receptive fields cover not more than 50 degrees out in the lower hemifield or on the horizontal meridian. In a few cases the periphery of the horizontal meridian and the upper hemifield are not at all represented in V3, or only in an incomplete manner.6. The magnification factors (Daniel & Whitteridge, 1961) become progressively smaller from V1 to V2 to V3. Hence cortical volume occupied decreases from V1 to V3. In V1 and in V2 the magnification is highest along the lower vertical meridian. In V2 the magnification along the horizontal meridian is the smallest, whereas in V1 the magnification decreases progressively from the lower vertical, to the horizontal and to the upper vertical meridian. The relationship between retinal ganglion cell densities and cortical magnification factors is discussed.

Animals↗
PubMed1979

14C-deoxyglucose mapping of orientation subunits in the cats visual cortical areas.

The orientation domain in the cortical visual areas of anesthetized cats has been investigated by employing the 14C-deoxyglucose technique (Sokoloff et al., 1977). Orientation subunits (OS) are seen in the first (V1), the second (V2) and the third visual area (V3) as well as in the visual areas of the suprasylvian sulcus. In the latter regions OS are less elaborated than in V1, V2, and V3. The OS are continuous through all cortical layers; in V1 however, only weak label is detected in layer 4C. In V1, V2, and V3 the width of the OS is about 0.4 mm and the average distance between two OS centers is 0.9 mm. The spatial pattern of the OS seems to be more regular in the visual field periphery than in regions representing the vertical meridian.

Animals↗
PubMed1978

Response variability and orientation discrimination of single cells in striate cortex of cat.

The response of single cells in the striate cortex of cat to a moving light bar of variable orientation was measured by a method providing data on the mean response as well as the standard deviation (SD) at the different stimulus orientations. At the optimal stimulus orientation the SD was about 1/3 of the mean response. Marked differences in this respect were found between simple and complex cells, i.e., the SD for the simple cells was about 1/2 of the mean response and about 1/4 for the complex cells. The variation coefficient (Vc = SD/mean) was minimal at the optimal orientation and increased relatively in the same manner for simple and complex cells as the stimulus orientation was varied away from optimal orientation. The Vc varied with the mean response at optimal orientation in a nonlinear manner. A function is proposed which fits this relationship and which is equally applicable for both simple and complex cells. The mean orientation discrimination (MOD) was defined as that change in orientation angle away from the optimal which produced a response statistically different--on the 1% level--from the response to the optimal orientation. There were differences in MOD between the two sides of the orientation tuning curve: the mean of the smaller of the two values was 13.5 deg and of the larger 19.7 deg. No significant difference in MOD was found between simple and complex cells despite the fact that the halfwidth of the tuning curves for the two cell types was 19.5 deg and 31.6 deg, respectively. The preciseness in localization of the most sensitive part within the receptive field of single cells was calculated from the variability in time of occurrence of the smallest interspike interval. The degree of preciseness was found to be of the order of 1/4 of the receptive field diameter in both simple and complex cells. When nonoptimal stimulus orientations were presented, the preciseness significantly decreased in complex cells whereas it remained unchanged in simple cells. It is suggested that the same type of intracortical wiring produces orientation selectivity in simple and complex cells, and that the differences in tuning width are mainly due to a larger extension of inhibitory fields in the simple cells. Considering the cortical visual cells as elementary units in a network built for orientation detection and discrimination, the tuning width seems of minor importance for that function.

Animals↗
PubMed1977

Cells of origin of the occipito-pontine projection in the cat: functional properties and intracortical location.

Extracellular records were taken from the areas 17, 18 and 19 of anaesthetized and immobilized cats. Of the 350 cells recorded in the cortical layers IV-VI, 22 responded with an antidromic action potential to electrical stimulation of the basal pontine region. Antidromic latencies ranged between 1.5-8.8 msec (mean and SD: 3.98 +/- 1.83 msec). The recording sites of these cells were in the cortical layer V. In the areas 17 and 18 of these cells were detected only in peripheral parts of the visual field representation. Some of these cells were tested with visual stimulation. They had complex receptive fields of large sizes, they received input from either eye, and their orientation selectively was relatively low. The sample of cells had neither a preference for a certain orientation nor for any particular degree of directional specifity nor for a certain range of movement velocity.

Animals↗
PubMed1977

The depth distribution of optimal stimulus orientations for neurones in cat area 17.

Neurones recording during penetrations through cat area 17 as near parallel to the radial fibre bundles as possible have been quantitatively tested as to their optimal orientation. Optimal orientation within any one penetration was similar though considerable variability was observed. Histological reconstruction and other considerations showed that this variability could not be attributed to poor penetration angle or limitations of the microelectrode technique. These results confirm that neurones with similar optimal orientations are found in all cortical layers at one cortical locus, but it is difficult to reconcile the variability observed with a mosaic-like distribution of orientation across the cortical surface. The findings were consistent, however, with the assumption of a continuous distribution of orientation sensitivity across the cortical surface with considerable superimposed scatter.

Animals↗
PubMed1975

A quantitative study of the projection area of the central and the paracentral visual field in area 17 of the cat. I. The precision of the topography.

1. In the course of long oblique penetrations through the postlateral gyrus a variation in the position of the receptive fields (RF-scatter) of single cells recorded extracellularly is observed. This is superimposed on the continuous topological representation of the retina. Spezifying the RF-positions by the azimuthal and elevation coordinates of their geometrical centers, the standard deviation (SD) of the mean RF-positions of cells recorded in 200 mum long horizontal sections of cortex is calculated and the total radial scatter of RF-positions (Sanderson, 1971) as defined: (see article) is determined. The radial scatter is found to have its smallest value (1 degree visual angle (v.a.)) in the projection area of the functional center of the area centralis increasing to 3-4 degrees v.a. at 10 degrees eccentricity. 2. The mean RF-diameter as defined: (see article) is centrally 0.7 degrees v.a. increasing to 2.6 degrees v.a. at 10 degrees eccentricity. The ratio of the largest RF-diameter to the smallest RF-diameter is between 7-9 and remains almost constant over the central 10 degrees of the projection area. The magnification factor (M) as defined: mm Cortex/degree v.a. is centrally 2.3, decreasing paracentrally to 0.6. 3. The cells in area 17 whose RFs have the same direction in the visual field constitute the spatial subunit of the retinocortical projection. The diameter of the spatial subunit is calculated as: (see article). The spatial subunit functionally represents, therefore, that part of the visual field whose location and area is calculated by averaging over the RFs of the individuals of its cell population. It is found that the cells belonging to a spatial subunit are distributed within a cortical cylinder of 2.6-2.8 mm in diameter, the peak of the distribution coinciding with the central axis of the cylinder. 4. Within the projection area of the central 10 degrees of the retina in area 17 the spatial subunits have the same diameter. This suggests that each retinal ganglion cell is functionally connected with an equal number of cells in area 17 irrespective of its position within the retina and that, therefore, the retinocortical projection is organized on the basis of a stereotyped schema if a basic spatial relationship is concerned.

Animals↗
PubMed1975

A quantitative study of the projection area of the central and the paracentral visual field in area 17 of the cat. II. The spatial organization of the orientation domain.

Cells in cat's area 17 respond optimally if elongated contrasts are presented at a certain angle or orientation with respect to the retina, or to the visual field, respectively (Hubel and Wiesel, 1962). The preferred orientation and the range of orientation sensitivity of cells in close proximity to one another have been determined in order to investigate the spatial arrangement of the orientation domain in area 17. 1. A slight overrepresentation of vertical and horizontal orientations is seen in cells with complex receptive fields, whereas in cells with simple fields all orientations are represented to an equal degree. The orientation selectivity, defined as the halfwidth of tuning curves constructed from the cells response to a moving stimulus, is less than 60 degrees in more than 80% of all cells investigated, and is on the average 20-30 degrees smaller in cells with simple than in cells with complex receptive fields. 2. In 80% of all cases considered the difference in the preferred orientation between two cells less than 200 mum horizontally distant in area 17 is less than 30 degrees, which is of the order of an individual cells orientation selectivity. Each cell, therefore, will respond to some extent to that orientation which is preferred by the cells in the immediate surroundings. 3. Sequential changes in the preferred orientation between cells successively recorded are observed as the postlateral gyrus is explored from anterior to posterior and from medial to lateral. On these general trends a random variation in the preferred orientation between neighbouring cells of the order of 5-10 degrees is superimposed. One orientation sequence (180 degrees) occupies 700-1200 mum, so that on the average a change in the preferred orientation of the order of 10 degrees is complete after 50 mum distance in the cortex measured parallel to the pial surface. Assuming that 18 different orientations (+/- 5 degrees) functionally represent one complete orientation sequence it is found that 'all' orientations are functionally represented by the cells contained in a cortical cylinder of 300-700 mum in diameter. 4. Cells having the same preferred orientation are grouped together in cortical regions which appear in crossection as a band or a spot. These regions have been termed iso-orientation bands or spots. The diameter of the spots and the small diameter of the bands do not exceed 100 mum. Taking an average orientation selectivity of 40 degrees for cells vertically aligned in area 17 it is calculated that cells situated 100 mum to either side of an iso-orientation band or around an iso-orientation spot still respond with 50% of the discharge to their own optimal orientation ...

Evoked Potentials↗