A quantitative study of the projection area of the central and the paracentral visual field in area 17 of the cat

Cells in cat's area 17 respond optimally if elongated contrasts are presented at a certain angle of 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 μm 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 μm, so that on the average a change in the preferred orientation of the order of 10 degrees is complete after 50 μm 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 μm 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 μm. Taking an average orientation selectivity of 40 degrees for cells vertically aligned in area 17 it is calculated that cells situated 100 μm 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. 5. The functional subunit of the orientation domain, the orientation subunit, consists of that cells which respond at all to a particular orientation. These cells are vertically aligned through all cortical layers (Hubel and Wiesel, 1963) and are located on the average 200 μm (range 25–450 μm) in a horizontal direction to either side from the center iso-orientation band or spot. The sensitivity to the orientation functionally represented by the subunit decreases with increasing distance from the center band, and from the center spot, respectively. The spatial properties of the subunit imply, that each subunit has indeterminate boundaries and that it shares cells with its immediate neighbours. From this it is concluded, that in most parts of area 17 of the cat there is a continuous orientation representation. 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. In 80% of all cases considered the difference in the preferred orientation between two cells less than 200 μm 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. 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 μm, so that on the average a change in the preferred orientation of the order of 10 degrees is complete after 50 μm 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 μm in diameter. 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 μm. Taking an average orientation selectivity of 40 degrees for cells vertically aligned in area 17 it is calculated that cells situated 100 μm 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. The functional subunit of the orientation domain, the orientation subunit, consists of that cells which respond at all to a particular orientation. These cells are vertically aligned through all cortical layers (Hubel and Wiesel, 1963) and are located on the average 200 μm (range 25–450 μm) in a horizontal direction to either side from the center iso-orientation band or spot. The sensitivity to the orientation functionally represented by the subunit decreases with increasing distance from the center band, and from the center spot, respectively. The spatial properties of the subunit imply, that each subunit has indeterminate boundaries and that it shares cells with its immediate neighbours. From this it is concluded, that in most parts of area 17 of the cat there is a continuous orientation representation.

[1]  V. Mountcastle Modality and topographic properties of single neurons of cat's somatic sensory cortex. , 1957, Journal of neurophysiology.

[2]  D. Hubel,et al.  Receptive fields of single neurones in the cat's striate cortex , 1959, The Journal of physiology.

[3]  D. Hubel,et al.  Receptive fields, binocular interaction and functional architecture in the cat's visual cortex , 1962, The Journal of physiology.

[4]  W. Levick,et al.  The determination of the projection of the visual field on to the lateral geniculate nucleus in the cat , 1962, The Journal of physiology.

[5]  D. Hubel,et al.  Shape and arrangement of columns in cat's striate cortex , 1963, The Journal of physiology.

[6]  D H HUBEL,et al.  RECEPTIVE FIELDS AND FUNCTIONAL ARCHITECTURE IN TWO NONSTRIATE VISUAL AREAS (18 AND 19) OF THE CAT. , 1965, Journal of neurophysiology.

[7]  G. F. Cooper,et al.  The angular selectivity of visual cortical cells to moving gratings , 1968, The Journal of physiology.

[8]  D. Hubel,et al.  Receptive fields and functional architecture of monkey striate cortex , 1968, The Journal of physiology.

[9]  M. Abeles,et al.  Functional architecture in cat primary auditory cortex: columnar organization and organization according to depth. , 1970, Journal of neurophysiology.

[10]  P. O. Bishop,et al.  Responses to visual contours: spatio‐temporal aspects of excitation in the receptive fields of simple striate neurones , 1971, The Journal of physiology.

[11]  D. Hubel,et al.  Sequence regularity and geometry of orientation columns in the monkey striate cortex , 1974, The Journal of comparative neurology.

[12]  P. O. Bishop,et al.  Orientation specificity of cells in cat striate cortex. , 1974, Journal of neurophysiology.

[13]  P. O. Bishop,et al.  Orientation, axis and direction as stimulus parameters for striate cells. , 1974, Vision research.

[14]  L. Palmer,et al.  Visual receptive fields of single striate corical units projecting to the superior colliculus in the cat. , 1974, Brain research.

[15]  K. Albus A quantitative study of the projection area of the central and the paracentral visual field in area 17 of the cat , 1975, Experimental brain research.

[16]  P. O. Bishop,et al.  Analysis of retinal correspondence by studying receptive fields of rinocular single units in cat striate cortex , 2004, Experimental Brain Research.

[17]  C. Blakemore,et al.  An analysis of orientation selectivity in the cat's visual cortex , 1974, Experimental Brain Research.

[18]  P. O. Bishop,et al.  Responses to moving slits by single units in cat striate cortex , 2004, Experimental Brain Research.