Postreinforcement electrocortical synchronization and enhancement of cortical photic evoked potentials during instrumentally conditioned appetitive behavior in the cat

Reticulo-cortical activity and behavior: A critique of the arousal theory and a new synthesis

It is traditionally believed that cerebral activation (the presence of low voltage fast electrical activity in the neocortex and rhythmical slow activity in the hippocampus) is correlated with arousal, while deactivation (the presence of large amplitude irregular slow waves or spindles in both the neocortex and the hippocampus) is correlated with sleep or coma. However, since there are many exceptions, these generalizations have only limited validity. Activated patterns occur in normal sleep (active or paradoxical sleep) and during states of anesthesia and coma. Deactivated patterns occur, at times, during normal waking, or during behavior in awake animals treated with atropinic drugs. Also, the fact that patterns characteristic of sleep, arousal, and waking behavior continue in decorticate animals indicates that reticulo-cortical mechanisms are not essential for these aspects of behavior.

These puzzles have been largely resolved by recent research indicating that there are two different kinds of input from the reticular activating system to the hippocampus and neocortex. One input is probably cholinergic; it may play a role in stimulus control of behavior. The second input is noncholinergic and appears to be related to motor activity; movement-related input to the neocortex may be dependent on a trace amine.

Reticulo-cortical systems are not related to arousal in the traditional sense, but may play a role in the control of adaptive behavior by influencing the activity of the cerebral cortex, which in turn exerts control over subcortical circuits that co-ordinate muscle activity to produce behavior.

Analgesia accompanying food consumption requires ingestion of hedonic foods

Animals eat rather than react to moderate pain. Here, we examined the behavioral, hedonic, and neural requirements for ingestion analgesia in ad libitum fed rats. Noxious heat-evoked withdrawals were similarly suppressed during self-initiated chocolate eating and ingestion of intraorally infused water, sucrose, or saccharin, demonstrating that ingestion analgesia does not require feeding motivation, self-initiated food procurement, sucrose, or calories. Rather, food hedonics is important because neither salt ingestion nor quinine rejection elicited analgesia. During quinine-induced nausea and lipopolysaccharide (LPS)-induced illness, conditions when chocolate eating was presumably less pleasurable, analgesia accompanying chocolate consumption was attenuated, yet analgesia during water ingestion was preserved in LPS-injected rats who showed enhanced palatability for water within this context. The dependence of ingestion analgesia on the positive hedonics of an ingestate was confirmed in rats with a conditioned taste aversion to sucrose: after paired exposure to sucrose and LPS, rats no longer showed analgesia during sucrose ingestion but continued to show analgesia during chocolate consumption. Eating pauses tended to occur less often and for shorter durations in the presence of ingestion analgesia than in its absence. Therefore, we propose that ingestion analgesia functions to defend eating from ending. Muscimol inactivation of the medullary raphe magnus blocked the analgesia normally observed during water ingestion, showing the involvement of brainstem endogenous pain inhibitory mechanisms in ingestion analgesia. Brainstem-mediated defense of the consumption of palatable foods may explain, at least in part, why overeating tasty foods is so irresistible even in the face of opposing cognitive and motivational forces.

Discrete neurochemical coding of distinguishable motivational processes: insights from nucleus accumbens control of feeding

BACKGROUND AND OBJECTIVES

The idea that nucleus accumbens (Acb) dopamine transmission contributes to the neural mediation of reward, at least in a general sense, has achieved wide acceptance. Nevertheless, debate remains over the precise nature of dopamine's role in reward and even over the nature of reward itself. In the present article, evidence is reviewed from studies of food intake, feeding microstructure, instrumental responding for food reinforcement, and dopamine efflux associated with feeding, which suggests that reward processing in the Acb is best understood as an interaction among distinct processes coded by discrete neurotransmitter systems.

RESULTS

In agreement with several theories of Acb dopamine function, it is proposed here that allocation of motor effort in seeking food or food-associated conditioned stimuli can be dissociated from computations relevant to the hedonic evaluation of food during the consummatory act. The former appears to depend upon Acb dopamine transmission and the latter upon striatal opioid peptide release. Moreover, dopamine transmission may play a role in 'stamping in' associations between motor acts and goal attainment and perhaps also neural representations corresponding to rewarding outcomes. Finally, evidence is reviewed that amino acid transmission specifically in the Acb shell acts as a central 'circuit breaker' to flexibly enable or terminate the consummatory act, via descending connections to hypothalamic feeding control systems.

CONCLUSIONS

The heuristic framework outlined above may help explain why dopamine-compromising manipulations that strongly diminish instrumental goal-seeking behaviors leave consummatory activity relatively unaffected.

Analysis of various factors involved in EEG synchronization during milk drinking in the cat

Electroencephalographic (EEG) and multineuronal activity (MUA) from several brain structures were recorded in 11 adult cats during milk drinking. Milk drinking elicited parietal and hippocampal EEG synchronization and inhibited multiunit discharge in several brain regions. The proportion of EEG synchronization varied considerably between animals, but remained more or less constant for each cat after several testing days. Neither modification of milk concentration nor fasting influenced the proportions of EEG synchronization during milk drinking. Adaptation of the animals to the experimental environment facilitated the appearance of EEG synchronization during milk drinking. Chlorpromazine (3 mg/kg) significantly increased the proportion of EEG synchronization observed during milk drinking. By contrast, displacement of the head, neck or postural body adjustments during milk drinking blocked EEG synchronization. Amphetamine also had a suppressive effect on the EEG parietal and hippocampal synchronic activity observed during milk drinking. Our results suggest that development of parietal EEG synchronization in response to pleasant stimulation is a complex phenomenon requiring a relaxed condition of the animal, including its adaptation to the experimental environment and relative immobility with the concomitant diminution of afferent inflow from some of the muscles involved in locomotion.