Local field potentials from different visual cortical areas and subdivisions of the cat's lateral posterior-pulvinar complex of the thalamus (LP-P) were recorded during a behavioral task based on delayed spatial discrimination of visual or auditory stimuli. During visual but not auditory attentive tasks, we observed an increase of ␤ activity (12-25 Hz) as calculated from signals recorded from the caudal part of the lateral zone of the LP-P (LPl-c) as well as from cortical areas 17 and 18 and the complex located at the middle suprasylvian sulcus (MSS). This ␤ activity appeared only in the trials that ended with a successful response, proving its relationship to the mechanism of visual attention. In contrast, no enhanced ␤ activity was observed in the rostral part of the lateral zone of the LP-P and in the pulvinar proper. Two subregions of LPl-c (ventromedial and dorsolateral) were distinguished by visually related, attentional ␤ activity of low (12-18 Hz) and high (18 -25 Hz) frequencies, respectively. At the same time, area 17 exhibited attentional activation in the whole ␤ range, and an increase of power in low-frequency ␤ was observed in the medial bank of MSS, whereas cortical area 18 and the lateral bank of the MSS were activated in the high ␤ range. Phase-correlation analysis revealed that two distinct corticothalamic systems were synchronized by the ␤ activity of different frequencies. One comprised of cortical area 17, ventromedial region of LPl-c, and medial MSS, the second involved area 18 and the dorsolateral LPl-c. Our observations suggest that LPl-c belongs to the wide corticothalamic attentional system, which is functionally segregated by distinct streams of ␤ activity.

The spatio-temporal frequency response profiles of 73 neurons located in the superficial, retino-recipient layers of the feline superior colliculus (SC) were investigated. The majority of the SC cells responded optimally to very low spatial frequencies with a mean of 0.1 cycles/degree (c/deg). The spatial resolution was also low with a mean of 0.31 c/deg. The spatial frequency tuning functions were either low-pass or band-pass with a mean spatial frequency bandwidth of 1.84 octaves. The cells responded optimally to a range of temporal frequencies between 0.74 cycles/s (c/s) and 26.41 c/s with a mean of 6.84 c/s. The majority (68%) of the SC cells showed band-pass temporal frequency tuning with a mean temporal frequency bandwidth of 2.4 octaves, while smaller proportions of the SC units displayed high-pass (19%), low-pass (8%) or broad-band (5%) temporal tuning. Most of the SC units exhibited simple spectral tuning with a single maximum in the spatio-temporal frequency domain, while some neurons were tuned for spatial or temporal frequencies or speed tuned. Further, we found cells excited by gratings moving at high temporal and low spatial frequencies and cells whose activity was suppressed by high velocity movement. The spatio-temporal filter properties of the SC neurons show close similarities to those of their retinal Y and W inputs as well as those of their inputs from the cortical visual motion detector areas, suggesting their common role in motion analysis and related behavioral actions.

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Oscillations are ubiquitous features of neuronal activity in sensory systems and are considered as a substrate for the integration of sensory information. Several studies have described oscillatory activity in the geniculate visual pathway, but little is known about this phenomenon in the extrageniculate visual pathway. We describe oscillations in evoked and background activity in the cat's superficial layers of the superior colliculus, a retinorecipient structure in the extrageniculate visual pathway. Extracellular single-unit activity was recorded during periods with and without visual stimulation under isoflurane anesthesia in the mixture of N2O/O2. Autocorrelation, FFT and renewal density analyses were used to detect and characterize oscillations in the neuronal activity. Oscillations were common in the background and stimulus-evoked activity. Frequency range of background oscillations spanned between 5 and 90 Hz. Oscillations in evoked activity were observed in about half of the cells and could appear in two forms —stimulus-phase-locked (10–100 Hz), and stimulus-phase-independent (8–100 Hz) oscillations. Stimulus-phase-independent and background oscillatory frequencies were very similar within activity of particular neurons suggesting that stimulus-phase-independent oscillations may be a form of enhanced “spontaneous” oscillations. Stimulus-phase-locked oscillations were present in responses to moving and flashing stimuli. In contrast to stimulus-phase-independent oscillations, the strength of stimulus-phase-locked oscillations was positively correlated with stimulus velocity and neuronal firing rate. Our results suggest that in the superficial layers of the superior colliculus stimulus-phase-independent oscillations may be generated by the same mechanism(s) that lie in the base of “spontaneous” oscillations, while stimulus-phase-locked oscillations may result from interactions within the intra-collicular network and/or from a phase reset of oscillations present in the background activity.