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 ...

SUMMARY1. The normal post-natal development of visual cortical functions was studied by recording extracellularly from 612 single neurones in the striate and parastriate cortex of anaesthetized and paralysed kittens, ranging in age from 6 to 24 days. Analyses have been made of laminar differences in the developmental trends of receptive field properties such as orientation specificity and spatial organization of 'on' and 'off' zones.2. At the beginning of the second post-natal week the majority of neurones (76 %) only respond to light 'off' (unimodal 'off' neurones). Only later does the frequency of occurrence ofunimodal 'on' neurones and of bimodal or multimodal neurones (with spatially segregated 'on' and 'off' zones arranged side by side) increase so that, by the middle of the fourth week, about equal numbers ofthese three receptive field types are found. The proportion of 'on-off' neurones (with spatially coincident 'on' and 'off' zones) remains low (between 9 % and 12 %) during the early post-natal period.3. In layers 4 and 6 of areas 17 and 18 the frequency of occurrence of visual neurones is quite normal even in the youngest kittens, whereas the probability of recording neurones in layers 2/3 and 5 in kittens less than 14 days old is remarkably low and only gradually improves up to the middle of the fourth week. A very rudimentary order in the spatial arrangement of orientation-specific neurones and ocular dominance distribution is observed even in very young kittens. This order improves rapidly and reaches adult levels during the fourth post-natal week.4. In visually inexperienced kittens, on average 11 % of all responsive neurones are selective for the orientation of elongated visual stimuli, and 58 % are biased. The proportion of orientation-selective cells begins to increase rapidly about two days after lid opening, and proportions of orientation-selective cells similar to that in the adult are reached by the end of the fourth post-natal week. Orientation-selective neurones in kittens less than 10 days old are only found in layers 4 and 6 and the lower part of layer 3. In layers 2/3 and 5 they are first seen in larger proportions by the beginning of the third post-natal week.5. Our results show that, during the first post-natal month, the time course of the functional development of visual cortical neurones depends on receptive field type

Gamma oscillations have been implicated in higher cognitive processes and might critically depend on proper mitochondrial function. Using electrophysiology, oxygen sensor microelectrode, and imaging techniques, we investigated the interactions of neuronal activity, interstitial pO 2 , and mitochondrial redox state [NAD(P)H and FAD (flavin adenine dinucleotide) fluorescence] in the CA3 subfield of organotypic hippocampal slice cultures. We find that gamma oscillations and spontaneous network activity decrease significantly at pO 2 levels that do not affect neuronal population responses as elicited by moderate electrical stimuli. Moreover, pO 2 and mitochondrial redox states are tightly coupled, and electrical stimuli reveal transient alterations of redox responses when pO 2 decreases within the normoxic range. Finally, evoked redox responses are distinct in somatic and synaptic neuronal compartments and show different sensitivity to changes in pO 2 . We conclude that the threshold of interstitial pO 2 for robust CA3 network activities and required mitochondrial function is clearly above the "critical" value, which causes spreading depression as a result of generalized energy failure. Our study highlights the importance of a functional understanding of mitochondria and their implications on activities of individual neurons and neuronal networks.

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.