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J Neurophysiol (November 1, 2002). 10.1152/jn.00858.2001
Submitted on 18 October 2001
Accepted on 2 August 2002
1Department of Biomedical Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel; 2Schepens Eye Research Institute, Boston, Massachusetts 02114; and 3Department of Ophthalmology, and 4Program in Neuroscience, Harvard Medical School, Boston, Massachusetts 02115
Kagan, Igor,
Moshe Gur, and
D. Max Snodderly.
Spatial Organization of Receptive Fields of V1 Neurons of Alert
Monkeys: Comparison With Responses to Gratings. J. Neurophysiol. 88: 2557-2574, 2002. We studied the
spatial organization of receptive fields and the responses to gratings
of neurons in parafoveal V1 of alert monkeys. Activating regions (ARs)
of 228 cells were mapped with increment and decrement bars while
compensating for fixational eye movements. For cells with two or more
ARs, the overlap between ARs responsive to increments (INC) and ARs
responsive to decrements (DEC) was characterized by a quantitative
overlap index (OI). The distribution of overlap indices was bimodal.
The larger group (78% of cells) was composed of complex cells with
strongly overlapping ARs (OI 
0.5). The smaller group (14%) was
composed of simple cells with minimal spatial overlap of ARs (OI 
0.3). Simple cells were preferentially located in layers dominated
by the magnocellular pathway. A third group of neurons, the
monocontrast cells (8%), responded only to one sign of contrast and
had more sustained responses to flashed stimuli than other cells. One
hundred fourteen neurons were also studied with drifting sinusoidal
gratings of various spatial frequencies and window widths. For complex
cells, the relative modulation (RM, the ratio of the 1st harmonic to the mean firing rate), ranged from 0.6 ± 0.4 to 1.1 ± 0.5 (mean ± SD), depending on the stimulus conditions and the
mode of correction for eye movements. RM was not correlated with the
degree of overlap of ARs, indicating that the spatial organization of
receptive fields cannot reliably be predicted from RM values. In fact,
a subset of complex cells had RM > 1, the traditional criterion for identifying simple cells. However, unlike simple cells, even those
complex cells with high RM could exhibit diverse nonlinear responses
when the spatial frequency or window size was changed. Furthermore, the
responses of complex cells to counterphase gratings were predominantly
nonlinear even harmonics. These results show that RM is not a robust
test of linearity. Our results indicate that complex cells are the most
frequently encountered neurons in primate V1, and their behavior needs
to receive more emphasis in models of visual function.
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