Food and intracranial stimulation responding suppressed with regular-interval shock.

Attenuation of conditioned suppression during intracranial stimulation was compared with that during food reinforcement. Response rates controlled by food and by brain stimulation were equalized on a multiple schedule by adjusting the stimulating current. When foot shock was delivered during timeout periods separating response components, responding for food was significantly more suppressed than responding for brain stimulation. When components were shortened from 10 to 2 minutes, responding maintained by either food or brain stimulation showed a similar temporal pattern of suppression preceding each shock, but responding in the component involving food remained significantly more suppressed. Explanations for the attenuated suppression during brain stimulation based on neural disruption, stimulus blocking, and analgesic properties were questioned. The increased responding during brain stimulation seemed to reflect greater response strength relative to food reinforced responding.     

Increased reinforcement when timeout from avoidance includes access to a safe place

Three experiments investigated the reinforcing value of access to a safe place during timeout from an avoidance schedule. Rats were trained on conjoint schedules in which responding both postponed shock on a free-operant avoidance schedule and produced periods of timeout on fixed-ratio schedules. In some conditions, a shelf was inserted into the operant chamber during timeout, enabling subjects to get off the grid floor. The combination of timeout and shelf maintained substantially higher response rates than the baseline avoidance schedule with ratio requirements as high as 90 (Experiment I). Adding the shelf to timeouts in one component of multiple fixed-ratio schedules of timeout resulted in higher response rates in the component where the shelf was included (Experiment II). When timeouts with and without the shelf were arranged on concurrent schedules, the shelf-timeout combination was preferred, even when of shorter duration than timeout alone (Experiment III). In all three experiments, subjects climbed on the shelf, although all shocks were cancelled during timeout periods. The results could not be accounted for solely in terms of the reinforcing properties of changes in shock rates, but required an interpretation that ascribed conditioned reinforcing value to stimuli associated with such changes.     

Escape from serial stimuli leading to food

If the functional relations governing the strength of a conditioned reinforcer correspond to those obtained with other Pavlovian procedures (e.g., Kaplan, 1984), the termination of stimuli appearing early in the interval between successive food deliveries should be reinforcing. During initial training we presented four key colors, followed by food, in a recurrent sequence to each of 6 pigeons. This established a baseline level of autoshaped pecking. In later sessions, we terminated each of these colors or only the first color for a brief period following each peck, replacing the original color with a standard substitute to avoid darkening the key. Pecking decreased in the presence of the last color in the sequence but increased in the presence of the first. In accord with contemporary models of Pavlovian conditioning, these and other data suggest that the behavioral effects of stimuli in a chain may be better understood in terms of what each stimulus predicts, as measured by relative time to the terminal reinforcer, than in the exclusively positive terms of the traditional formulation (Skinner, 1938). The same model may also account for the initial pause under fixed-interval and fixed-ratio schedules of reinforcement.     

Input-specific long-term potentiation in the rat lateral amygdala of horizontal slices

Long-term potentiation (LTP) at input synapses to the lateral nucleus of the amygdala (LA) is a candidate mechanism for memory storage during fear learning. Cellular mechanisms of LTP have been nearly exclusively investigated in coronal brain slices. In our experiments, we used a horizontal brain slice preparation of rats that preserved most of the connections to cortical areas and the hippocampus. The stimulation electrodes were located either within the external capsule (EC) or the LA. The aim of the present study was to investigate the mechanisms of LTP induced either by weak theta burst stimulation (TBS) or strong high frequency stimulation (HFS) using the two different stimulation sites. Whereas both TBS and HFS of afferences running through the LA induced stable LTP, TBS failed to induce LTP of EC-inputs to the LA. The present findings also show that LTP in the LA exhibits vulnerability at different time windows after induction. The time window was dependent on the kind of stimulated afferences. Later LTP becomes resistant to disruption by low frequency stimulation. We could show that both used inputs depended on NMDA receptors for LTP-induction. LTP induced by stimulation of fibers within the LA was not altered by nifedipine (10 microM). In contrast, EC-induced LTP was dependent on L-type voltage-gated calcium channels (VGCC). Finally, we found a higher magnitude of LTP in females using TBS, whereas HFS did not cause gender-specific differences. Our study supports the conclusion that the form of LA-LTP depend on which afferences are activated and what pattern of stimulation is used to induce LTP.     

Enhancing Creativity With Combined Transcranial Direct Current and Random Noise Stimulation of the Left Dorsolateral Prefrontal Cortex and Inferior Frontal Gyrus

Creativity is a fundamental human accomplishment from scientific advances to composing music. The left dorsolateral prefrontal cortex (DLPFC) and inferior frontal gyrus (IFG) are important metacontrol hubs in flexibility and persistence brain states, respectively. Those hubs are related to divergent thinking, insight problem-solving, and convergent thinking. In this double-blind, between-subjects study, 81 healthy participants were randomly assigned to one of three groups (n = 27) that received a combined transcranial direct current stimulation–transcranial random noise stimulation (tDCS-tRNS) protocol with the anode over the left DLPFC and cathode over the left IFG (+DLPFC−IFG), the opposite montage (−DLPFC+IFG), and a sham group (+DLPFC−IFG). Both active tDCS-tRNS groups received 20 min of 1 mA tDCS with 1 mA (100–500 Hz) tRNS. Creativity was assessed before (baseline) and during stimulation with the Unusual Uses, Picture Completion (PC), Remote Association test (RAT), Matchstick Arithmetic (MA), and Nine-dot (ND) problems. Only the +DLPFC−IFG group had significantly higher scores compared with sham in the RAT (p = .009), PC fluency (p = .018), PC originality (p = .007), ND (p = .007), and MA (p = .032). Overall, −DLPFC+IFG had greater scores in all creativity tests compared with sham. Implications from the metacontrol theory are discussed.     

Concurrent schedules: Quantifying the aversiveness of noise

Four hens worked under independent multiple concurrent variable-interval schedules with an overlaid aversive stimulus (sound of hens in a poultry shed at 100dBA) activated by the first peck on a key. The sound remained on until a response was made on the other key. The key that activated the sound in each component was varied over a series of conditions. When the sound was activated by the left (or right) key in one component, it was activated by the right (or left) key in the other component. Bias was examined under a range of different variable-interval schedules, and the applicability of the generalized matching law was examined. It was found that the hens' behavior was biased away from the sound independently of the schedule in effect and that this bias could be quantified using a modified version of the generalized matching law. Behavior during the changeover delays was not affected by the presence of the noise or by changes in reinforcement rate, even though the total response measures were. Insensitivity shown during the delay suggests that behavior after the changeover delay may be more appropriate as a measure of preference (or aversiveness) of stimuli than are overall behavior measures.     

Positive and negative reinforcement effects on behavior in a three-person microsociety

Three-person groups, either of males or of females, resided for 6 to 12 days in a continuously programmed environment. Subjects followed a behavioral program that determined the sequential and contingent relations within an inventory of activities. The program consisted of positive reinforcement days and avoidance days. During a positive reinforcement day, each work unit completed by a subject incremented a group account. The account was divided evenly among the three participants at the conclusion of the study. During a negative reinforcement day, no money was earned, and the group was assigned work unit criterion that, if completed, prevented a reduction in accumulated earnings. During negative reinforcement days, subjects made aggressive verbal responses, which differed in magnitude among the four groups. These differences were evident in several distinct behavioral measures. Performances on components of the work unit were not demonstrably affected by the reinforcement schedules in effect, although during the avoidance condition one subject stopped working and another subject's productivity declined.     

THE EFFECTS OF MATCHED STIMULATION AND RESPONSE INTERRUPTION AND REDIRECTION ON VOCAL STEREOTYPY

Stereotypy has been classified as repetitive behavior that does not serve any apparent function. Two procedures that have been found to reduce rates of vocal stereotypy effectively are response interruption and redirection (RIRD) and noncontingent access to matched stimulation (MS). The purpose of the current study was to evaluate the effects of RIRD alone, MS alone, and MS combined with RIRD. One participant's results suggested similar suppressive effects on vocal stereotypy across treatment conditions. For the second participant, a slightly greater suppression of stereotypy was associated with MS + RIRD. In addition, both participants emitted a greater frequency of appropriate vocalizations in conditions with RIRD. Data suggest that the addition of MS might facilitate the implementation of RIRD in applied settings.