Figure 1.

Comparison of oscillations in awake ventral striatum and other interconnected regions. A) Coronal rat brain sections showing an example of simultaneous tetrode placements in medial frontal cortex (mPFC; #1), ventral striatum (Str; #2-6), piriform cortex (Piri; #7) and dorsal hippocampus (Hipp; 8-9). B) Local field potentials recorded from the locations shown in A) during performance of a radial maze task. Also shown are ECoG recordings from skull screws placed over ipsilateral olfactory bulb (AP 7, ML 1 mm relative to bregma) and frontal cortex (AP 5, ML 2.5 mm). All signals are referenced to the same location (see Methods). Note theta (~8Hz) rhythm that is most prominent in deep hippocampal layers (#9) and large amplitude high-frequency oscillation (~50Hz) that is most prominent in piriform cortex and nearby regions of ventral striatum, and also visible to a lesser degree in olfactory bulb ECoG. C) (Top) Power spectral density and (bottom) coherence plots for a subset of the recording sites illustrated in A,B. In all cases coherence was calculated to LFP at site #4.. Coherence is high for all frequencies when comparing sites within ventral striatum, but resolves into more discrete frequency bands when comparing ventral striatum to other structures. D) Mean coherence spectra between ventral striatal LFP and: another site in ventral or central striatum (left, light blue); dorsal hippocampus CA1 pyramidal layer (left, dark blue); frontal cortex ECoG (right, dark green); olfactory bulb ECoG (right, light green). n = 7 (all rats for which all of these signals were simultaneously recorded). Each plot shows mean +− S.E.M. (shaded area). Points immediately surrounding 60Hz are omitted due to occasional contributions of line noise. Coherence is high for all frequencies between two striatal sites, but is selective to theta oscillations between striatum and hippocampal CA1. Coherence in the high-gamma range is consistently higher between striatum and frontal cortex ECoG than between striatum and olfactory bulb ECoG, or between striatum and posterior cortex ECoG (not shown).