Aims: 

The hypothesis was tested that neurons in the rat medial prefrontal cortex may respond to reward predicting stimuli before drinking of solutions with high reward value.

Methods: 

In the present experiments multiple unit recordings (8 tetrodes) were made in the mPFC of freely moving Wistar rats during consumption of sugar solution or water in a 24-sec fixed interval paradigm. Different tones predicted the different solutions.

Results: 

267 single unites were separated. 108 neurons responded to at least one event. The following response patterns were observed: 1. excitation or inhibition during sugar solution or water consumption (37 neurons); 2. excitation or inhibition before sugar solution or water consumption (24 neurons); 3. inhibition at the beginning of the predicting tone and excitation of the same neuron during sugar solution or water consumption (32 neurons); 4. excitation at the beginning of the predicting tone and delay period (7 neurons); 5. excitation after removing the drinking bottle (8 neurons). Neurons responded more often to sugar solution then to water.

Conclusion: 

We demonstrated that neurons in the rat mPFC respond specifically to reward predicting external stimuli. Other neurons respond in relation to reward consumption. About half of neurons respond during both phases, reward expectation and reward consumption as well. Our data suggest that the rat mPFC has a significant role in guiding reward related behavior.

Support: 

NKTH-OTKA K68431 and the HAS