Single neuron activity was recorded from the monkey anterior cingulate cortex during operant behavior based on discrimination of rewarding, aversive, and neutral objects. Of 550 neurons recorded, 116 responded during the task; 36, during visual discrimination; 40, during bar pressing for operant responding. Of these, 26 vision-related neurons responded differentially to rewarding, aversive and neutral objects, and 11 bar press-related neurons differentiated bar pressing to avoid shock from bar pressing to obtain reward. Responses of these neurons depended on associative meaning (aversive or rewarding) of the objects since these neuronal responses were modulated by the reversal learning. The results provide neuronal bases for involvement of the anterior cingulate cortex in emotional and motivational processes.