DYNAMIC PROPERTIES OF CORTICOTHALAMIC NEURONS AND LOCAL CORTICAL INTERNEURONS GENERATING FAST RHYTHMIC (30-40 HZ) SPIKE BURSTS

Dynamic properties of corticothalamic neurons and local cortical inter neurons generating fast rhythmic (30-40 Bz) spike-bursts. J. Neurophys iol. 79: 483-490, 1998. Fast spontaneous oscillations (mainly 30-40 Hz ) characterize cortical and thalamic neuronal networks during behavior al states of increased vigilance and depend on cell depolarization und er the influence of ascending activating systems. We investigated, by means of intracellular recording and staining in vivo, the properties of fast-oscillating cortical neurons from cat's motor and association areas, some projecting to the thalamus, others with locally arborizing axons. At a given level of depolarization, 28% of our neuronal sample discharged high-frequency spike bursts (300-600 Hz) that recurred rhy thmically between 20 and 50 Hz. Such fast rhythmic bursting neurons ha ve been found in both superficial and deep cortical layers. Slight cha nges in membrane potential as well as synaptic activity in thalamocort ical networks dramatically altered the discharge patterns, from single spikes to rhythmic spike-bursts, and eventually to fast tonic firing without frequency adaptation. Thus our data challenge the conventional idea that sharply defined, invariant features and distinct locations in certain cortical layers characterize some neocortical cell-classes. We demonstrate that the distinctions between intrinsic electrophysiol ogical properties of neocortical neurons are much more labile than con ventionally thought. The present results, which indicate that corticot halamic neurons discharge fast rhythmic spike bursts mainly at 30-40 H z, suggest that this activity results in integrated fast oscillations within corticothalamic networks.