SPATIAL PHASE AND THE TEMPORAL STRUCTURE OF THE RESPONSE TO GRATINGS IN V1

Citation
Jd. Victor et Kp. Purpura, SPATIAL PHASE AND THE TEMPORAL STRUCTURE OF THE RESPONSE TO GRATINGS IN V1, Journal of neurophysiology, 80(2), 1998, pp. 554-571
Citations number
77
Categorie Soggetti
Neurosciences,Physiology
Journal title
ISSN journal
00223077
Volume
80
Issue
2
Year of publication
1998
Pages
554 - 571
Database
ISI
SICI code
0022-3077(1998)80:2<554:SPATTS>2.0.ZU;2-3
Abstract
We recorded single-unit activity of 25 units in the parafoveal represe ntation of macaque V1 to transient appearance of sinusoidal gratings. Gratings were systematically varied in spatial phase and in one or two of the following: contrast, spatial frequency, and orientation. Indiv idual responses were compared based on spike counts, and also accordin g to metrics sensitive to spike timing. For each metric, the extent of stimulus-dependent clustering of individual responses was assessed vi a the transmitted information, H. In nearly all data sets, stimulus-de pendent clustering was maximal for metrics sensitive to the temporal p attern of spikes, typically with a precision of 25-50 ms. To focus on the interaction of spatial phase with other stimulus attributes, each data set was analyzed in two ways. In the ''pooled phase'' approach, t he phase of the stimulus was ignored in the assessment of clustering, to yield an index H-pooled. In the ''individual phases: approach, clus tering was calculated separately for each spatial phase and then avera ged across spatial phases to yield an index H-indiv. H-pooled expresse s the extent to which a spike train represents contrast, spatial frequ ency, or orientation in a manner which is not confounded by spatial ph ase (phase-independent representation), whereas H-indiv expresses the extent to which a spike train represents one of these attributes, prov ided spatial phase is fixed (phase-dependent representation). Here, re presentation means that a stimulus attribute has a reproducible and sy stematic influence on individual responses, not a neural mechanism for decoding this influence. During the initial 100 ms of the response, c ontrast was represented in a phase-dependent manner by simple cells bu t primarily in a phase-independent manner by complex cells. As the res ponse evolved, simple cell responses acquired phase-independent contra st information, whereas complex cells acquired phase-dependent contras t information. Simple cells represented orientation and spatial freque ncy in a primarily phase-dependent manner, but also they contained som e phase-independent information in their initial response segment. Com plex cells showed primarily phase-independent representation of orient ation but primarily phase-dependent representation of spatial frequenc y. Joint representation of two attributes (contrast and spatial freque ncy, contrast and orientation, spatial frequency and orientation) was primarily phase dependent for simple cells, and primarily phase indepe ndent for complex cells. In simple and complex cells, the variability in the number of spikes elicited on each response was substantially gr eater than the expectations of a Poisson process. Although some of thi s variation could be attributed to the dependence of the response on t he spatial phase of the grating, variability was still markedly greate r than Poisson when the contribution of spatial phase to response vari ance was removed.