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Units of monkey superior colliculus responding to complex visual stimuli
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Units of monkey superior colliculus responding to complex visual stimuli H. A. BUCHTEL, R. CAMARDA, G. RIZZOLATTI and C. SCANDOLARA - - lstituto di Fisiologia Umana, Universit&di Parma, 43100 Parma (Italy)
Single-unit activity was recorded in the superior colliculus of awake curarized monkeys (Macaca irus). In addition to movement-sensitive, non-directionally selective units 1,2,3, we have found other units which were poorly or not at all triggered by the traditional light and dark two-dimensional stimuli, but which responded vigorously to the presentation of complex moving or stationary stimuli (especially three-dimensional objects) ~. The responses were not specific to a particular object, but some objects were more effective than others. Gradual habituation of the response after repeated presentation of the object was always found, but subsequent presentation of a new object in the receptive field produced a brisk response and in some units dishabituated the response to the old stimulus. Extrafield presentation of a new stimulus never had this effect, nor was there habituation to objects presented repeatedly outside the receptive field and then within the receptive field. This last finding makes it very unlikely that the effects are related to general arousal. These results suggest that units in the superior colliculus of the monkey are capable of distinguishing between different objects and that their firing rate reflects the newness of the stimulus. Further experiments are in progress to clarify the importance of cortico-collicular pathways in determining this discriminative capacity. 1 Goldberg, M. E. and Wurtz, R. H., J. Neurophysiol., 35 (1972) 542 559. 2 Schiller, P. H. and Koerner, F., J. NeurophysioL, 34 (1971) 920-936. 3 Updyke, B. V., J. Neurophysiol., 37 (1974) 896-910.
Thermal sensitization of cutaneous polymodal nociceptors in the monkey S. CROZE and R. DUCLAUX - - Laboratoire de Physiologie, Facult~ de M~decine, Lyon Sud-Ouest, B.P. 12, 69600 Oullins (France)
Polymodal nociceptors in hairy skin of the monkey were submitted to two successive series of thermal stimuli by a Peltier stimulator placed on the receptor field 1. Each series included 4 successive temperature changes from 37 or 33 °C up to 43, 45, 47 and 50 °C at a rate of 0.2 °C/sec. Mean discharge characteristics of the population of receptors (n ~ 13) was compared during the two series of hot stimulation. During the first series, the mean discharge threshold was 42.5 °C, peak frequency increased linearly as a function of the intensity of heating, and the mean number of impulses during temperature change increased as a power function with an exponent higher than one as a function of the intensity of the stimulus. This latter result indicates that impulse frequency accelerates from threshold to maximum temperature change. During the second series of stimulations, most of the fibres were more sensitive to temperature changes. The mean discharge threshold was decreased to 38.8 °C. The mean peak frequency and the total impulses count during temperature change was
Units of monkey superior colliculus responding to complex visual stimuli H. A. BUCHTEL, R. CAMARDA, G. RIZZOLATTI and C. SCANDOLARA - - lstituto di Fisiologia Umana, Universit&di Parma, 43100 Parma (Italy)
Single-unit activity was recorded in the superior colliculus of awake curarized monkeys (Macaca irus). In addition to movement-sensitive, non-directionally selective units 1,2,3, we have found other units which were poorly or not at all triggered by the traditional light and dark two-dimensional stimuli, but which responded vigorously to the presentation of complex moving or stationary stimuli (especially three-dimensional objects) ~. The responses were not specific to a particular object, but some objects were more effective than others. Gradual habituation of the response after repeated presentation of the object was always found, but subsequent presentation of a new object in the receptive field produced a brisk response and in some units dishabituated the response to the old stimulus. Extrafield presentation of a new stimulus never had this effect, nor was there habituation to objects presented repeatedly outside the receptive field and then within the receptive field. This last finding makes it very unlikely that the effects are related to general arousal. These results suggest that units in the superior colliculus of the monkey are capable of distinguishing between different objects and that their firing rate reflects the newness of the stimulus. Further experiments are in progress to clarify the importance of cortico-collicular pathways in determining this discriminative capacity. 1 Goldberg, M. E. and Wurtz, R. H., J. Neurophysiol., 35 (1972) 542 559. 2 Schiller, P. H. and Koerner, F., J. NeurophysioL, 34 (1971) 920-936. 3 Updyke, B. V., J. Neurophysiol., 37 (1974) 896-910.
Thermal sensitization of cutaneous polymodal nociceptors in the monkey S. CROZE and R. DUCLAUX - - Laboratoire de Physiologie, Facult~ de M~decine, Lyon Sud-Ouest, B.P. 12, 69600 Oullins (France)
Polymodal nociceptors in hairy skin of the monkey were submitted to two successive series of thermal stimuli by a Peltier stimulator placed on the receptor field 1. Each series included 4 successive temperature changes from 37 or 33 °C up to 43, 45, 47 and 50 °C at a rate of 0.2 °C/sec. Mean discharge characteristics of the population of receptors (n ~ 13) was compared during the two series of hot stimulation. During the first series, the mean discharge threshold was 42.5 °C, peak frequency increased linearly as a function of the intensity of heating, and the mean number of impulses during temperature change increased as a power function with an exponent higher than one as a function of the intensity of the stimulus. This latter result indicates that impulse frequency accelerates from threshold to maximum temperature change. During the second series of stimulations, most of the fibres were more sensitive to temperature changes. The mean discharge threshold was decreased to 38.8 °C. The mean peak frequency and the total impulses count during temperature change was