Fig. 1.

Progressive development of low-frequency oscillations within the STN during baseline recording, i.e., in absence of cocaine (15 min before access to cocaine) parallels escalation of cocaine intake. a Schematic of the experiment. b Increase in cocaine intake during the first 30 min of self-administration averaged by blocks of five daily sessions over ShA (black bar: days 1–5, blue bar: days 6–10) and LgA conditions (green bar: days 1–5, red bar: days 6–10, purple bar: days 11–15; block effect: F_4,20 = 6.952, P = 0.011, n = 6, repeated measure one-way ANOVA). c Daily time-frequency analysis of the power spectrum, equivalent to a measurement of the signal amplitude. Values indicate the ratio of power spectrum normalized to the first day of ShA. d–f Highlights (upper panels, bold lines indicate average power values, light-colored areas indicate SEM; LgA 6–10 data have been omitted for clarity of presentation) and global quantifications of baseline power (bottom panels) for the theta (d), beta (e), and gamma (f) bands. Cocaine escalation induces an increase in oscillation power during LgA sessions only in the theta and beta bands (d F_4,20 = 4.308, P < 0.05; e F_4,20 = 4.633, P < 0.01; f F_4,20 = 1.917, n.s., repeated measures one-way ANOVA). All bars are mean with SEM. *P < 0.05, **P < 0.01 vs. ShA 1–5 (Bonferroni post hoc test)