Intelligence and Information Processing

The relationship between mental ability (MA, Raven Progressive Matrices) and speed of information processing was examined by recording mismatch negativity (MMN) parameters from 41 women during passive listening to auditory standard and deviant stimuli with backward masking. The intertone interval (ITI) between the offset of the standard or deviant tone and the onset of the masking tone was varied between conditions (25, 50, or 150 ms). Three versions of a trail-making test (Zahlen-Verbindungs-Test, ZVT) were also presented to obtain a behavioral index of information processing speed. Multiple regression analysis showed that the more difficult versions of the ZVT and midline frontal MMN latency at 25-ms ITI were both significant predictors of MA. Across all ITI conditions, the higher ability (HA) group exhibited a shorter MMN latency than the lower ability (LA) group. Finally, the HA group also had a larger MMN amplitude than the LA group for the 25-ms ITI condition. These results indicate that low-level auditory discrimination, indexed by MMN, contributes to individual differences in fluid intelligence. In this regard, MMN provides a valuable tool for examining individual differences in intelligence in individuals who are not able to comply with psychometric testing.

Differences Between Accumbens Core and Shell Neurons Exhibiting Phasic Firing Patterns Related to Drug-Seeking Behavior During a Discriminative-Stimulus Task

The habit-forming effects of abused drugs depend on the mesocorticolimbic dopamine system innervating the nucleus accumbens (NAcc). To examine whether different NAcc subterritories (core and medial shell) exhibit a differential distribution of neurons showing phasic firing patterns correlated with drug-seeking behavior, rats were trained to self-administer cocaine, and activity of single NAcc neurons was recorded. In the presence of a discriminative-stimulus (SD) tone, a single lever press produced an intravenous infusion of cocaine (0.35 mg/kg), terminated the tone, and started an intertone interval ranging from 3 to 6 min. Lever presses during this intertone interval had no programmed consequences. In addition to evaluating neuronal firing patterns associated with cocaine-reinforced presses, we also evaluated firing patterns associated with unreinforced lever presses to allow interpretation of firing free of factors other than the instrumental response (such as tone-off and onset of the pump signaling drug infusion). Core neurons exhibited a greater change in firing than medial shell neurons both in the seconds preceding the reinforced and unreinforced lever press response and in the seconds following the unreinforced response. Core and medial shell neurons exhibited similar changes in firing during the seconds following the cocaine-reinforced press. The differential distribution of neurons exhibiting phasic changes in firing preceding the lever press suggests that the physiological activity of core neurons may play a greater role than that of medial shell neurons in processes related to the execution of conditioned drug-seeking responses.