Discharge properties of neurons in subdivisions of the medial geniculate body of the guinea pig

The activity of 194 neurons was recorded in three subdivisions of the media l geniculate body (74 neurons in the ventral, 62 in the medial and 44 neuro ns in the dorsal subdivision, i.e. vMGB, mMGB and dMGB) of guinea pigs anes thetized with ketamine-xylazine. The discharge properties of neurons were e valuated by means of peristimulus time histograms (PSTHs), interval histogr ams (INTHs) and auto-correlograms (ACGs). In the whole MGB, the most freque nt PSTH responses to pure tone stimuli were onset (43 %) or chopper (32 %). The onset responses were mostly present in the vMGB, whereas chopper respo nses dominated in the dMGB. In the whole MGB Poisson-like and bimodal INTHs were found in 46 % and 40 % of neurons, respectively. The mMGB revealed fe wer bimodal and more symmetrical types of INTH. In the whole MGB, 60 % of u nits were found to have ACGs typical for short bursts (<100 ms), 23 % for l ong bursts (>100 ms) and 15 % of units fired without bursts. Neurons in the vMGB were characterized by short bursting, whereas those in the mMGB and d MGB expressed more activity in the long bursts. The results demonstrate tha t the type of information processing in the vMGB, which belongs to the "pri mary" auditory system, is different from that in two other subdivisions of the MGB.