Barbiturate spindle activity in functionally corresponding thalamic and cortical somato-sensory areas in the cat.

(1) Spontaneous barbiturate spindles were recorded from a locus in the thalamic nucleus ventralis postero-lateralis (VPL) and the corresponding projection area in the somato-sensory cortex (SI) in the cat. (2) Type I spindles32 recorded from such sites in the thalamus and cortex, regarded as being functionally on line, were cross-correlated. The analysis gave high negative cross-correlation coefficients, indicating that a considerable degree of wave synchrony existed between the spindles. Maximal wave synchrony was present in the first and middle part of the spindle. (3) The thalamo-cortical spindle wave synchrony was reduced by a small displacement of the cortical electrode within the somato-sensory cortex. Starting with a very lightly anaesthetized animal, small amounts of barbiturate did not influence the size of the cortical area which had spindles in synchrony with the thalamic spindles. (4) Spindles recorded from a VPL locus and from its cortical projection site started simultaneously. When the thalamic and cortical electrodes were positioned functionally off line this spindle coincidence decreased. The intervals between the spindle onsets increased with increasing off line positions of the electrodes. Those few thalamic and cortical spindles which occurred simultaneously showed no, or only weak, spindle wave synchrony. (5) These data suggest a point-to-point topographical relation between thalamic and cortical loci engaged in barbiturate spindle activity. (6) Type I and type II spindles32 differed with respect to spindle characteristics (amplitude, duration, incidence) and also with respect to corresponding thalamic rhythmic activity. These spindle types are, therefore, probably produced by different mechanisms. We suggest that type II spindles represent a purely cortical process initiated by type I spindles.     

Preoptic area unit activity during sleep and wakefulness in the cat

The spontaneous discharge of 86 preoptic area (POA) neurons was recorded extracellularly in chronically prepared cats during wakefulness (W), slow-wave sleep (SWS), and REM sleep. Of these, the percentage of units exhibiting maximal discharge rates in SWS and REM sleep (84%) was significantly greater than that of those exhibiting a maximal discharge rate in W (16%). Furthermore, those neurons that discharged rapidly in sleep (fast units) generally had a reduced discharge rate in W. Sixteen of the 86 units showed a strong tendency to discharge in bursts during SWS but not during W or REM sleep. The mean coefficient of variation and the mean discharge rate for these bursting cells in SWS were significantly greater than the corresponding values for the same cells in W and REM sleep, and for the nonbursting cells in SWS. Because POA stimulation is known to initiate behavioral and electrocortical signs of sleep, it is suggested that "fast units" in SWS with reduced discharge rates in W, may be "hypnogenic" cells.     

Degeneration of some intralaminar thalamic nuclei after cortical removals in the cat

• 1 The projections of the central medial, paracentral, and central lateral nuclei of the cat have been studied by the method of retrograde degeneration.
• 2 Following removal of neocortex, with preservation of rhinencephalic and sub-cortical structures, the central medial, paracentral, and central lateral nuclei degenerate severely.
• 3 The central medial and paracentral nuclei degenerate only after extensive cortical lesions which include limbic cortex. There is evidence of a topographical organization of the projection since rostral sectors of central medial and paracentral nuclei show cell loss after lesions involving anterior limbic and orbitofrontal cortex while caudal sectors degenerate after lesions involving cingulate and parieto-occipital cortex.
• 4 The central lateral nucleus projects to cortex of the parieto-occipital region.
• 5 Some findings are considered which indicate that fibers from the central medial, paracentral, and central lateral nuclei travel rostrally to the region of the head of the caudate nucleus before turning caudally to distribute to cortical areas.

     

The effects of a spirolactone derivative on EEG and cortical single unit activity in the cat.

With systemic (60-150 mg/kg) and topical application, Aldactone exhibited strong convulsant action on the cat cerebral cortex. The most common abnormal interictal features of the surface ECoG pattern were sequences of fast waves and slow negative waves associated with positive sharp waves, negative field potentials and burst-like neuronal activation in the extracellular microelectrode record. Another abnormal pattern was a period of ECoG and neuronal inactivity subsequent to the negative transients. These series of sharp and slow waves and of inactivity were interrupted by tonic and clonic ECoG seizures characterized by regular surface positive spikes. Development of seizures, but not of interictal phenomena, could be prevented by intravenous application of Diazepam (1 mg), Nembutal (30 mg/kg) and--less effectively--by Phenhydane (20 mg/kg).     

Dynamics of EEG spindle frequency activity during extended sleep in humans: relationship to slow-wave activity and time of day

The dynamics of EEG spindle frequency activity (SFA; spectral power density in the 12.25–15.0 Hz range) and its relationship to slow-wave activity (SWA; 0.75–4.5 Hz) were investigated in long sleep episodes (>12 h). Young healthy men went to bed at either 19:00 h (early sleep; prior waking 36 h, n=9) or 24:00 h (late sleep; prior waking 17 h, n=8). In both nights, SWA in non-rapid-eye-movement sleep (NREMS) decreased over the first three to four 1.5-h intervals and remained at a low level in the subsequent five to six 1.5-h intervals. In contrast, the changes of SFA were more variable and differed between the lower (12.25–13.0 Hz), middle (13.25–14.0 Hz) and higher frequency bin (14.25–15.0 Hz). A pronounced influence of time of day was present in the lower and higher SFA bin, when the dynamics were analyzed with respect to clock time. In both the early and late sleep condition, power density in the lower bin was highest between 2:00 and 5:00 h in the morning and decreased thereafter. In the higher bin, power density was low in the early morning hours and increased as sleep was extended into the daytime hours. The results provide further evidence for a frequency-specific circadian modulation of SFA which becomes more evident at a time when SWA is low.     

Simultaneous intracerebral EEG recordings of early auditory thalamic and cortical activity in human

We describe documented simultaneous intracerebral auditory evoked potentials from the auditory cortex and medial geniculate body (MGB) of a human patient. The MGB response lasted > 300 ms, with an initial negativity at 13.5 ms (N13), two positive peaks P21 and P29, and two broader negativities N50 and N200. P21 and N50 amplitudes were strongest for lowest tone frequencies, suggesting possible MGB tonotopic organization. Thalamic peaks were strongly interlaced with cortical activities recorded in Heschl's gyri before 30 ms: N13 preceded the first cortical component by 3.5 ms, then P21 and P29 preceded and lagged, respectively, the following two cortical polarity reversals by 1.5-2 ms. This study provides new functional data on the human MGB, and supports a more complex than simply relay-like role of the thalamus in sound perception.     

Changes in spontaneous activity of medialis dorsalis thalamic neurones during sleep and wakefulness

In chronic unanaesthetized cats unitary activity of medialis dorsalis (MD) thalamic neurones was recorded during wakefulness (W), slow wave (SWS) and desynchronized (DS) sleep. The discharge pattern of these neurones changes during SWS compared to W. Comparison between desynchronization of W and DS shows a change in the mean frequency, being higher in W than in DS. The results suggest that MD neurones participate in the organization of the sleep-wakefulness cycle.     

Small-world network organization of functional connectivity of EEG slow-wave activity during sleep.

OBJECTIVE: To analyze the functional connectivity patterns of the EEG slow-wave activity during the different sleep stages and Cyclic Alternating Pattern (CAP) conditions, using concepts derived from Graph Theory. METHODS: We evaluated spatial patterns of EEG slow-wave synchronization between all possible pairs of electrodes (19) placed over the scalp of 10 sleeping healthy young normal subjects using two graph theoretical measures: the clustering coefficient (Cp) and the characteristic path length (Lp). The measures were obtained during the different sleep stages and CAP conditions from the real EEG connectivity networks and randomized control (surrogate) networks (Cp-s and Lp-s). RESULTS: Cp and Cp/Cp-s increased significantly from wakefulness to sleep while Lp and Lp/Lp-s did not show changes. Cp/Cp-s was higher for A1 phases, compared to B phases of CAP. CONCLUSIONS: The network organization of the EEG slow-wave synchronization during sleep shows features characteristic of small-world networks (high Cp combined with low Lp); this type of organization is slightly but significantly more evident during the CAP A1 subtypes. SIGNIFICANCE: Our results show feasibility of using graph theoretical measures to characterize the complexity of brain networks during sleep and might indicate sleep, and the A1 phases of CAP in particular, as a period during which slow-wave synchronization shows optimal network organization for information processing.     

EEG frequency and time domain mapping study of the cortical projections of temporal lobe amygdala afterdischarge during kindling in the cat.

EEG frequency and time domain color maps were computed during amygdala kindling in cats. The pattern of the amygdala afterdischarge (AM/AD) propagation to the cortex was assessed as kindling evolved. Our results show that the AM/AD has 4 components that coincide with the activation of certain cortical areas during specific behavioral stages. The pattern of the cortical projection follows an asymmetrical temporo-fronto-occipital direction, the ipsilateral temporal lobe being the first activated zone, followed by the ipsilateral and contralateral prefrontal areas. The contralateral temporal activation is a late phenomenon. We conclude that the electrographic and behavioral manifestations of this model of complex partial epilepsy are asymmetrical during the whole process, including the convulsive stage.     

Topographic analysis of coherence and propagation of EEG activity during sleep and wakefulness

Overnight sleep EEG recorded from 21 derivations was studied in 8 healthy subjects. The vector autoregressive model was fitted to all 21 channels simultaneously. Ordinary, multiple and partial coherences and directed transfer functions were estimated for sleep stages and wakefulness. Ordinary coherences give rather trivial information that coherence decreases with distance. Partial coherences revealed specific structure that was well repeatable for the subjects studied. Differences in coherence patterns between sleep stages were found by means of statistical tests. An increase of coherence was found for sleep stages 2, 3 and 4. Directed transfer function made possible the identification of the main centers from which EEG activity is spreading during sleep and wakefulness. During sleep the influence of subcortical structures was manifested by propagation of activity from then fronto-central region. The range of this interaction was highest in sleep stages 3 and 4. An EEG analysis, based on the approach of treating time series as a realization of one process and on the simultaneous (not pair-wise) evaluation of signals offers new possibilities in the investigation of synchronization and functional relations in the brain.     

Power spectral analysis of EEG activity obtained from cortical and subcortical sites during the vigilance states of the cat

There is considerable evidence that the raphe system and the region of the nucleus tractus solitarious (NTS), including the area postrema, play significant roles in slow-wave sleep mechanisms and in EEG synchronization. Studies of the interactions between these systems and the neocortex are much needed. If neuronal activity in these lower brainstem regions regulates the degree of cortical synchrony then a high degree of correspondence between the EEG of the area postrema or raphé complex with that of the cortex might be expected. In order to quantitate the frequency characteristics of the EEG obtained from these subcortical sites (nucleus raphé dorsalis, area postrema, as well as anatomical controls adjacent to these regions) during the different vigilance states (waking, slow-wave sleep, REM sleep) in the cat, power spectral analyses techniques were employed. Comparison of these subcortical spectral characteristics with those obtained from cortical (frontal and occipital) sites during the same vigilance state, show that the spectral measures elicited from the region of the area postrema closely correspond to that of the cortex, particularly during slow-wave sleep. On the other hand, the EEG of the anterior portion of the raphé region, although exhibiting a substantial low frequency component during slow-wave sleep in comparison to wakefulness does not show a statistically significant shift to low frequencies such as occurs in the area postrema or the cortex. These results suggest that the increases in the low frequency content of the cortical EEG sites during slow-wave sleep results from synchronizing inputs from the area postrema to a greater extent than from the raphé complex.     

Pattern processing and slow-wave activity in visual cortex of cat

Animal models play a significant role in research on human disorders. In vision research, the recording of single-neuron activity from animals has been of great value to our understanding of pattern processing mechanisms. In humans, investigations of visual function have typically utilized slow-wave activity. We have studied in cats the relationship between pattern processing and the slow-wave evoked response recorded from cortical areas 17, 18, 19 and 4 in the awake cat. We have found that within a restricted latency range the response in 17, 18 and 19 reflects the processing of the patterness of a visual stimulus. A comparison of response components occurring prior to 50 msec poststimulus showed few significant differences (P less than 0.05) between peak amplitudes evoked by a diffuse and a checkerboard pattern stimulus. A much higher proportion of response components occurring after 50 msec but prior to 300 msec poststimulus were significantly different (P less than 0.05). The response recorded from area 4 (motor cortex) did not show significant differences as a function of the diffuse and patterned stimuli. Our findings show that the slow wave recorded from cat visual cortex can reflect the pattern processing mechanisms of visual cortex. Since slow waves are used in the study of visual functions in humans, the slow wave may have an important role to play in animal models of visual disorders in humans.     

Changes in EEG spindle activity induced by ibotenic acid lesions of medialis dorsalis thalamic nuclei in the cat

The injection of an excitotoxin into medialis dorsalis thalamic nuclei (MD) elicited a short-term increase followed by a depression on EEG spindle waves in chronically implanted cats. This biphasic action provides further evidence to the hypothesis that MD plays a crucial role in transferring and inducing spindling on frontal cortex. In addition, retrograde horseradish peroxidase transport from previously lesioned MD labeled subcortical structures such as basal forebrain, anterior hypothalamus, reticular thalamic nucleus, ventral tegmental area, and locus coeruleus.     

Effects of noradrenaline on frequency tuning of auditory cortex neurons during wakefulness and slow-wave sleep.

This study shows the effects of noradrenaline (NA) on receptive fields of auditory cortex neurons in awake animals; it is the first one to describe the effects of NA on neurons in sensory cortex, in different natural states of vigilance. The frequency receptive field of 250 auditory cortex neurons was determined before, during and after ionophoretic application of NA while recording the state of vigilance of unanaesthetized guinea-pigs. When NA significantly changed the spontaneous activity (85 out of 250 cells), the dominant effect was a decrease (61 out of 85 cells, 72%). When NA significantly changed the evoked activity (107 out of 250 cells), the dominant effect was also a decrease (84 out of 107 cells, 78%). During and after NA application, the signal-to-noise ratio (S/N, i.e. evoked/spontaneous activity) was unchanged, but the selectivity for pure-tone frequencies was enhanced. When the effects occurring in wakefulness and in slow-wave sleep (SWS) were compared, it appeared that the predominantly inhibitory effect of NA on spontaneous and evoked activity was present in both states. The S/N ratio was unchanged and the selectivity was increased in both states. However, during SWS, the percentage of cells inhibited by NA was lower, and the effects on the frequency selectivity were smaller than in wakefulness. In contrast, GABA produced similar inhibitory effects on spontaneous and on evoked activity during wakefulness and SWS. Comparisons with previous data obtained using the same protocol in urethane anaesthetized animals (Manunta & Edeline 1997) indicate that the effects of NA were qualitatively the same. Based on these results, we suggest that any hypothesis concerning the role of NA in cortical plasticity should take into account the fact that the predominantly inhibitory effects of NA lead to decrease the size of the receptive field.