Two sets of experiments examine the psychological functions and neural organization of the frontal lobes. The first set investigates the effects of lesions of the frontal cortex (FC) on the ability to perform temporal discriminations, using the techniques and theoretical framework of scalar timing theory. FC lesions changed the reference memory for the expected time of reinforcement, so that rats expected reinforcement later than it actually occurred. These results demonstrate that the FC modulates temporal memory. The second set of experiments examined the behavioral effects of lesions in the nucleus basalis magnocellularis (NBM), an area in the basal forebrain that has a significant projection to the frontal cortex. NBM lesions produced impairments in many different tasks assessing both recent and long-term memory. A comparison of the behavioral and neurochemical effects of different types of lesions in the NBM examines the role of cholinergic and noncholinergic neurotransmitters in these behavioral deficits. These data demonstrate that a "frontal syndrome" can follow selective lesions in the NBM, and indicate that the NBM must have a strong role in frontal lobe function.