Electrical activity in the prefrontal cortex specific to no-go reaction of conditioned hand movement with colour discrimination in the monkey

Summary Monkeys were trained to perform hand movements in a reaction time task with discrimination between positive (go) and negative (no-go) light signals, and field potentials in various cortical areas were recorded and analysed with chronically implanted cortical electrodes. As previously reported, areas such as the prefrontal, premotor and motor cortices were active in association with simple visually-initiated, reaction-time hand movements. The caudal part of the dorsal bank of the principal sulcus was found to be activated specifically on no-go trials during discrimination, and revealed a relatively sharp surface-negative, depth-positive potential. The potential appeared at a latency of 110–150 ms, which was 150–210 ms earlier than the movement onset on go trials. With reversal of the go and no-go signals, this potential was found to be recorded only on no-go trials, irrespective of the colour used for the stimulus. It is suggested that the activity in the dorsal bank of the principal sulcus is related to the judgement not to execute the movement and/or the suppression of motor execution.     

The asymmetries in morphology, desoxyribonucleic acid, protein and ribonucleic acid of the two hemispheres induced by monolateral removal of the olfactory bulb and retrobulbar structures in neonatal rats

Monolateral removal of the olfactory bulb and the olfactory penduncular structures in the neonatal rat resulted in a profound morphological and biochemical asymmetry between the two hemispheres. The experimental hemisphere, ipsilateral to the lesion, protruded into the space normally occupied by the olfactory bulb and showed enlarged ventricles. The brain loci were displaced rostrally in this hemisphere.The desoxyribonucleic acid, ribonucleic acid and protein contents of the experimental hemisphere at 25 and 60 days of age were all significantly lower than that found in the control hemisphere contralateral to the lesion.To resolve between the two possible causes of this asymmetry (i.e. atrophy of the experimental or hypertrophy of the control hemisphere) hemispheres of the asymmetric brain were compared with homonymous hemispheres of unoperated normal rats. This comparison revealed that the asymmetry is basically due to an excess of desoxyribonucleic acid synthesis in the control hemisphere, which continues even after postnatal day 25, on the one hand, and a dearth of protein in the experimental hemisphere on the other. This finding implies two separate mechanisms for the processes that underlie the asymmetries observed for these two substances.Our results demonstrate two important characteristics of the developing brain. Firstly they indicate that removal of the olfactory bulb and the olfactory peduncle can produce considerable changes in the hemispheres, and secondly they unravel the strong latent potential of the brain for cell proliferation beyond the usual period of cell division in the brain. As in these experiments regulation of cell division is affected, this system might serve as a model for the study of aberrant cell division found in tumor formation and the process of carcinogenesis.     

A biological context for the self-nonself discrimination and the regulation of effector class by the immune system

An effective immune response to an antigen requires two sets of decisions: Decision 1, the sorting of the repertoire, and Decision 2, the regulation of effector class. The repertoire, because it is somatically generated, large, and random, must be sorted by a somatic mechanism that subtracts those specificities (anti-self) that, if expressed, would debilitate the host, leaving a residue (anti-nonself) that, if not expressed, would result in the death of the host by infection. The self-nonself discrimination is the metaphor used to describe Decision 1, the sorting of the repertoire. In order to be functional, the sorted repertoire must be coupled to a set of biodestructive and ridding effector functions, such that the response to each antigen is treated in a coherent and independent manner. Although a reasonably complete framework for Decision 1 exists, Decision 2 lacks conceptualization. The questions that must be considered to arrive at a proper framework are posed. It should be emphasized that manipulation at the level of Decision 2 is where clinical applications are likely to be found.     

Operant conditioning studies of taste discrimination in the pigeon (Columba livia)

In the conditioning procedure employed in this study, pigeons were trained to dip their bills into a container and then to peck either at a left or at a right key, depending on whether the container was full of distilled water or of a solution of the substance being tested. The discrimination thresholds found (from one bird each) were 2 g/l (0.034 M) for NaCl, 2 g/l (0.024 M) for NaHCO₃, 1 g/l (0.013 M) for KCl, 0.5 g/l (0.005 M) for KHCO₃. Following the same procedure, two birds were then faced with the choice between the solution of the known substance and of a novel one. A higher degree of discrimination was found between NaHCO₃ and KHCO₃ than between NaHCO₃ and NaCl; in the latter case, choices appeared to be mostly based on the concentration of the two substances.     

Differential fos activation in virgin and lactating mice in response to an intruder

Lactating (L) mice display fierce aggression towards novel, male mice, while virgin (V) mice do not. This study compares patterns of brain activation in V and L mice in response to a novel intruder using immunohistochemical detection of Fos (Fos-IR). Animals were sampled 120 min after either a sham or real 10 min test with a male intruder. L mice were aggressive towards intruders, but V mice were not. In general, Fos-IR for both groups increased with exposure to an intruder, with L mice showing higher increases in Fos-IR than V mice. In only medial preoptic nucleus and ventral portion of bed nucleus of stria terminalis (BNST) was Fos-IR significantly increased in both groups with testing. In V mice, testing resulted in Fos-IR increases in an additional 10 regions examined that did not reach significance in L mice, including lateral septum, lateral and medial preoptic areas, and anterior hypothalamus. Fos-IR also increased with testing in nine regions unique to L mice, including the mitral and granular layers of accessory olfactory bulb, regions of the amygdala, dorsal BNST, and caudal portions of the hypothalamic attack area. These increases in Fos-IR with testing suggest alterations in the circuitry governing response to pheromonal cues and imply some commonalities between the circuitries governing maternal aggression and intermale aggression. These results support the hypothesis that pregnancy and lactation induce substantial changes in brain circuitry and function; changes that enable maternal defense of offspring by altering the neural response to an intruder male.     

Latent inhibition of conditioned odor potentiation of startle: a developmental analysis

We conducted a two-part study of age and latent inhibition in the rat. In the first part of the study, rats given odor-shock pairings at 23 or 75 days of age exhibited a potentiated startle response in the presence of the odor the following day. This effect did not occur in rats trained at 16 or 20 days of age. Odor pre-exposure on the day prior to conditioning markedly reduced the odor potentiation of startle effect in 23- and 75-day-old rats but had no effect in 16 and 20-day-olds. In the second part of the study, rats were pre-exposed to the odor at 16 or 20 days of age and then conditioned at 23 days of age. When tested the day after conditioning, these pre-exposed rats exhibited a disruption in the odor potentiation of startle effect. We compare our results with other studies of latent inhibition, and with recent studies on whether conditioned responses are appropriate to the animal's age at training or their age at test.     

Calretinin- and parvalbumin-immunoreactive neurons in the rat main olfactory bulb do not express NADPH-diaphorase activity

The presence of nitric oxide synthase (NOS) in neuronal elements expressing the calcium-binding proteins calretinin (CR) and parvalbumin (PV) was studied in the rat main olfactory bulb. CR and PV were detected by using immunocytochemistry and the nitric oxide (NO) -synthesizing cells were identified by means of the reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) direct histochemical method. The possible coexistence of NADPH-diaphorase and each calcium-binding protein marker was determined by sequential histochemical-immunohistochemical double-labeling of the same sections. Specific neuronal populations were positive for these three markers. A subpopulation of olfactory fibers and olfactory glomeruli were positive for either NADPH-diaphorase or CR. In the most superficial layers, groups of juxtaglomerular cells, superficial short-axon cells and Van Gehuchten cells demonstrated staining for all three markers. In the deep regions, abundant granule cells were NADPH-diaphorase- and CR-positive and a few were PV-immunoreactive. Scarce deep short-axon cells demonstrated either CR-, PV-, or NADPH-diaphorase staining. Among all these labeled elements, no neuron expressing CR or PV colocalized NADPH-diaphorase staining. The present data contribute to a more detailed classification of the chemically- and morphologically-defined neuronal types in the rodent olfactory bulb. The neurochemical differences support the existence of physiologically distinct groups within morphologically homogeneous populations. Each of these groups would be involved in different modulatory mechanisms of the olfactory information. In addition, the absence of CR and PV in neuronal groups displaying NADPH-diaphorase, which moreover are calmodulin-negative, indicate that the regulation of NOS activity in calmodulin-negative neurons of the rat olfactory bulb is not mediated by CR or PV.     

Spontaneous activity of single neurons in the olfactory bulb of the rainbow trout (Salmo gairdneri) and its modulation by olfactory stimulation with amino acids

Summary Spontaneous action potentials recorded from 126 neurons in the olfactory bulb of Salmo gairdneri show a higher tendency towards bursting patterns of activity than those shown in previous reports about other fish. Granule cells and periglomerular cells are more likely to fire in bursts than mitral cells. Natural chemical stimulation of the olfactory mucosa with amino acid solutions produced a unique pattern of excitatory and inhibitory responses across all units. Chi-square values were calculated for stimulatory effectiveness between forty-five pairs of odours. L-serine and L-alanine consistently showed a high degree of similarity with several other odours. The converse was true for GABA and L-histidine, although this pair had a high chi-square value when mutually compared. Enantiomeric pairs of amino acids were often found to have opposite stimulatory effects on bulbar units. These results are discussed in relation to the possible properties and configurations of odorant receptor sites for amino acids in the fish olfactory mucosa.     

Effects of the presentation of false heart-rate feedback on the performance of two common heartbeat-detection tasks.

Research has indicated that performance on heartbeat counting tasks may be influenced by beliefs about heart rate. Sixty male subjects were administered the Schandry heartbeat counting task after viewing fast, slow, or no heart rate feedback. Subjects were also administered the Whitehead signal-detection type task. Results indicated that subjects who received fast or no heartbeat feedback performed better on the Schandry task than subjects who received slow feedback. Feedback presentation did not affect performance on the Whitehead task. These results suggest that the Schandry task is influenced by external variables (expectations, beliefs) beyond pure awareness of "discrete" visceral sensations and, thus, may not be as powerful a method for determining awareness of individual heartbeats as some other paradigms.     

Auditory Discrimination and the Eyeblink

This experiment evaluated the association between blinking and cognitive activities. Subjects received 200 and 400 ms tones (1 KHz) at fixed intervals in a duration discrimination paradigm. One group (“Task”) was instructed to respond to the stimuli on the basis of duration and another (“No-Task”) was instructed to ignore the stimuli. Blink activity (latency, rate, duration) and performance (RT, hit and false alarm rates) measures were evaluated. A first analysis (Task subjects only) indicated that stimulus duration had significant effects on RT and blink latency; both were generally longer following the 400-ms than the 200-ms stimuli. In a second analysis, involving Task and No-Task subjects, blink latencies were shorter in the Task group. Blink and eyelid closure durations increased over the task period in both analyses. These effects suggest that blinks occur when attentional processes wane.