Basic properties of neocortical delta rhythms in vitro in human and rat tissue. A, Linear electrode array recording of persistent, spontaneous delta rhythms in rat parietal cortex. Image shows a 2 s epoch of delta activity as current source density plot. Note the superficial dominance of sink/source pairs. Graphs show mean delta power (n = 5, with 5 × 20 s epochs per n) and laminar phase difference relative to layer 5. Note the power maxima in layer 5 (as seen in human recordings in C) and the abrupt phase reversal between layers 1 and 2/3. Example trace taken from an electrode located in layer 5. Calibration: 0.3 mV, 1 s. B, Pharmacological profile of delta activity. i, Incidence of spontaneous delta generation with neuromodulation. Con, Control; Carb, carbachol, 2 μm; SCH, SCH23390, 10 μm. ii, Changes in mean delta power (n = 5) after application of drugs affecting various network mechanisms: pirenzipine (Pir, 10 μm) M1/M3 blockade, AP-5 (50 μm) NMDAR blockade, NBQX (20 μm) AMPA/kainate receptor blockade, SYM2206 (SYM, 10 μm) AMPAR blockade, UBP302 (UBP, 20 μm) GluR5 kainate receptor blockade, gabazine (Gbz, 500 nm) GABAA receptor blockade, CGP55845 (CGP, 1 μm) GABAB receptor blockade, and gap junction conductance decrease [carbenoxolone (Cbx, 0.2 mm), octanol (Oct, 1 mm), quinine (Qui, 0.2 mm), and 18β-glycyrrhetinic acid (Gly, 0.1 mm)]. C, Voltage-sensitive dye imaging of persistent, spontaneous delta rhythms in human frontal cortex. Image shows delta power averaged over 5 × 20 s epochs. Color map adjusted to show delta power hard-thresholded at 30 dB. Graph shows mean laminar distribution of delta power indicating maxima in layers 5/6 and 2/3. Example trace shows a 2 × 2 pixel binned time series of the raw fluorescence change. Calibration: 0.02% δF/F, 1 s.