Reversal learning in pigeons: Effects of selective lesions of the Wulst.

Evaluated the effects of bilateral lesions of individual laminae of the Wulst on reversal-learning performance in pigeons. After surgery, Ss were trained to perform a simultaneous color discrimination. Once successful discrimination was achieved, the positive and negative stimuli were reversed, and Ss were again trained to criterion. 20 reversals were carried out. A multiple regression analysis indicated that those components of the Wulst that were critical for increasing the numbers of errors on each reversal were the laminae that receive the thalamofugal visual projections (i.e., the nucleus intercalatus of the hyperstriatum accessorium and the hyperstriatum dorsale). Lesions in the other laminae of the Wulst (the hyperstriatum accessorium and the hyperstriatum intercalatus superior) had no effect on errors. There was no evidence of an increase in either perseverative errors or position habits in the Ss with lesions, suggesting that the reversal deficits were not likely to be due to perseveration, attentional impairment, or inappropriate processing of spatial information. The deficit may have been produced by excessive interference between learning in a given session and learning in previous sessions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impairment of cingulothalamic learning-related neuronal coding in rabbits exposed to cocaine in utero: General and sex-specific effects.

Neuronal activity was recorded in the cingulate cortex and the limbic thalamus in Dutch-belted rabbits (Oryctolagus cuniculus) exposed to cocaine (8 mg/kg/day iv) or saline in utero during acquisition and reversal learning of a discriminative avoidance response. Anterior cingulate cortical excitatory training-induced activity (TIA) was attenuated in cocaine-exposed female rabbits during acquisition and reversal learning, but only during reversal learning in male rabbits. Posterior cingulate cortical excitatory TIA was lessened in cocaine-exposed rabbits during acquisition, whereas discrimination between the positive and negative cues was enhanced. Neuronal firing was attenuated in the anterior ventral thalamus in cocaine-exposed rabbits during acquisition and reversal learning. Behavioral learning was normal in cocaine-exposed rabbits. Other data suggest that rabbits exposed to cocaine in utero exhibit a learning deficit when trained with nonsalient cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Representations of odors in the rat orbitofrontal cortex change during and after learning.

Cells in the orbitofrontal cortex (OF) respond to odors and their associated rewards. To determine how these responses are acquired and maintained, the authors recorded single OF units in rats performing an odor discrimination task. Approximately 64% of all cells differentiated between rewarded and nonrewarded odors. These odor valence responses changed during learning in 26% of all cells, and these changes were positively correlated with improving performance, supporting the idea that the information provided by these cells is used in learning the task. However, changes in odor valence responses were also observed after learning, and included not only increases in odor discrimination, but also decreases or mixed increases and decreases. Thus, only some of the changes in firing reflected acquisition of the task. The results suggest that learning triggers a continuing reorganization of OF neural ensembles representing odors and their rewards. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phasic firing time locked to cocaine self-infusion and locomotion: dissociable firing patterns of single nucleus accumbens neurons in the rat

The activity of single nucleus accumbens (NAcc) neurons of rats was extracellularly recorded during intravenous cocaine self-administration sessions (0.7 mg/kg per infusion, fixed ratio 1). We reported previously that NAcc neurons showed a change, usually a decrease, in firing rate during the first 1 min after the cocaine-reinforced lever press. This postpress change was followed by a progressive reversal of that change, which began within the first 2 min after the press and was not complete until the last 1 min before the next lever press (termed the change + progressive reversal firing pattern). In the present study we documented a regular pattern of locomotion that occurred in parallel with the change + progressive reversal firing pattern. This observation suggested that discharges time locked to locomotion may determine the change + progressive reversal firing pattern. However, 55% of the neurons failed to show firing time locked to locomotion that could have contributed to the change + progressive reversal firing pattern. Moreover, for all neurons, the change + progressive reversal firing pattern was apparent even if the calculation of firing rate excluded all periods of locomotion. The present data showed that the change + progressive reversal firing pattern is not solely attributable to phasic changes in firing time locked to the execution of locomotion. The change + progressive reversal firing pattern closely mirrors changes in drug level and dopamine overflow observed by previous researchers and may thus be a component of the neurophysiological mechanism by which drug level regulates drug-taking behavior during an ongoing self-administration session.     

Reactions and properties of the receptive fields of neurons in the visual projection zone of the pigeon hyperstriatum

Impulse responses of neurons of the pigeon forebrain hyperstriatal part to stationary and moving visual stimuli were investigated. Particular attention was given to revealing a retinotopic projection in the region of visual representation in Wulst. It is shown that as the electrode moved gradually in the caudal direction in the region of visual projection of the hyperstriatum, the receptive fields of the neurons under observation displaced in the visual field in the opposite direction. The receptive fields of the ventral and dorsal hyperstriatum cells remain higher in the visual field and have larger diameters than the receptive fields of neurons of the accessory hyperstriatum. Neurons responses of the visual projection of the Wulst region depend on luminosity, size, speed and direction of the movement of the test-objects through the receptive field. The functional role of the retino-thalamo-telencephalic system in the visual integration in birds is discussed and a supposition is advanced on possibility to compare the Wulst region with striatal and frontal visual areas of the mammalian cortex.     

Conditioned responses of monkey locus coeruleus neurons anticipate acquisition of discriminative behavior in a vigilance task

Impulse activity was recorded extracellularly from noradrenergic neurons in the nucleus locus coeruleus of three cynomolgus monkeys performing a visual discrimination (vigilance) task. For juice reward, the subjects were required to release a lever rapidly in response to an improbable target stimulus (20% of trials) that was randomly intermixed with non-target stimuli presented on a video display. All locus coeruleus neurons examined were phasically and selectively activated by target stimuli in this task. Other task events elicited no consistent response from these neurons (juice reward, lever release, fix spot stimuli, non-target stimuli). With reversal of the task contingency, locus coeruleus neurons ceased responding to the former target stimuli, and began responding instead to the new target (old non-target) stimuli. In addition, the latency of locus coeruleus response to target stimuli increased after reversal (by about 140 ms) in parallel with a similar increase in the latency of the behavioral response. These results indicate that the conditioned locus coeruleus responses reflect stimulus meaning and cognitive processing, and are not driven by physical sensors attributes. Notably, the reversal in locus coeruleus response to stimuli after task reversal occurred rapidly, hundreds of trials before reversal was expressed in behavioral responses. These findings indicate that conditioned responses of locus coeruleus neurons are plastic and easily altered by changes in stimulus meaning, and that the locus coeruleus may play an active role in learning the significance of behaviorally important stimuli.     

Intensity difference thresholds after lesions of the visual Wulst in pigeons.

Studied visual intensity difference thresholds before and after telencephalic lesions in 8 White Carneaux pigeons. Ss with visual Wulst lesions showed initial postoperative threshold elevations that represented losses of 19–49% of their preoperative sensory capacity. This initial loss was correlated with the extent of damage to 3 components of the visual Wulst: nucleus intercalatus hyperstriati accessorii, hyperstriatum intercalatus suprema, and hyperstriatum accessorium. The damage to hyperstriatum dorsale, another component of the visual Wulst, made no contribution to the initial deficit. The sensory capacity of all but 1 S improved as a result of postoperative retraining. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

NMDA and D2-like receptors modulate cognitive flexibility in a color discrimination reversal task in pigeons.

Reversal and extinction learning represent forms of cognitive flexibility that refer to the ability of an animal to alter behavior in response to unanticipated changes on environmental demands. A role for dopamine and glutamate in modulating this behavior has been implicated. Here, we determined the effects of intracerebroventricular injections in pigeons' forebrain of the D2-like receptor agonist quinpirole, the D2-like receptor antagonist sulpiride and the N-methyl-d-aspartate receptor antagonist AP-5 on initial acquisition and reversal of a color discrimination task. On day one, pigeons had to learn to discriminate two color keys. On day two, pigeons first performed a retention test, which was followed by a reversal of the reward contingencies of the two color keys. None of the drugs altered performance in the initial acquisition of color discrimination or affected the retention of the learned color key. In contrast, all drugs impaired reversal learning by increasing trials and incorrect responses in the reversal session. Our data support the hypothesis that D2-like receptor mechanisms, like N-methyl-d-aspartate receptor modulations, are involved in cognitive flexibility and relearning processes, but not in initial learning of stimulus-reward association. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exercise improves memory acquisition and retrieval in the Y-maze task: Relationship with hippocampal neurogenesis.

Enhanced physical activity is associated with improvements in cognitive function in rodents as well as in humans. The authors examined in detail which aspects of learning and memory are influenced by exercise, using a spatial Y-maze test combined with a 14-day exercise paradigm at different stages of learning. The authors show that 14 days of wheel running promotes memory acquisition, memory retention, and reversal learning. The exercise paradigm that was employed also significantly increased the number of maturing neurons, suggesting that an increase in neurogenesis underlies the positive effects of exercise on Y-maze performance. Finally, the authors show that memory acquisition in itself does not have a major impact on the number of immature neurons. However, memory retention testing and reversal learning both cause a significant reduction in the number of doublecortin and Ser133- phosphorylated pCREB-positive cells, indicating that a decrease in neurogenesis might be a prerequisite for optimal memory retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental changes in the voltage-dependence of neocortical NMDA responses

A change in the response of neocortical neurons to N-methyl-D-aspartate (NMDA) was observed during the first 2 weeks of postnatal development. When NMDA was bath applied, the membrane current-voltage relationship recorded in neurons from postnatal day (PN) 3-5 rats displayed a region of decreased inward current at hyperpolarized membrane potentials. By PN 9-14, the net inward current at hyperpolarized potentials was significantly less than that recorded in PN 3-5 neurons. These results indicate that a developmental increase in the voltage-dependence of NMDA responses exists, which may be due to changes in magnesium sensitivity of the NMDA receptor.     

Directionally selective mnemonic properties of neurons in the lateral dorsal nucleus of the thalamus of rats

The hippocampal formation has been extensively studied for its special role in visual spatial learning and navigation. To ascertain the nature of the associations made, or computations performed, by hippocampus, it is important to delineate the functional contributions of its afferents. Therefore, single units were recorded in the lateral dorsal nucleus of the thalamus (LDN) as rats performed multiple trials on a radial maze. Many LDN neurons selectively discharged when an animal's head was aligned along particular directions in space, irrespective of its location in the test room. These direction-sensitive cells were localized to the dorsal aspect of the caudal two-thirds of the LDN, the site of innervation by retinal recipient pretectal and intermediate/deep-layer superior colliculus cells (Thompson and Robertson, 1987b). The directional specificity and preference of LDN cells were disrupted if rats were placed on the maze in darkness. If the room light was then turned on, the original preference was restored. If the light was again turned off, directional firing was maintained briefly. Normal directional firing lasted about 2-3 min. After this time, the directional preference (but not specificity) appeared to "rotate" systematically in either the clockwise or counterclockwise direction. The duration of normal directional discharge patterns in darkness could be extended to 30 min by varying the behavior of the animal. LDN cells required visual input to initialize reliable directional firing. After the rat viewed the environment, directional specificity was maintained in the absence of visual cues. Maximal directional firing was achieved only when the rat viewed the entire test room, and not just the scene associated with the directional preference of the cell. Thus, contextual information seems important. Also, a significant correlation was found between directional specificity and errors made on the maze during acquisition of the task. It was concluded that the LDN may pass on to the hippocampal formation directional information that is not merely a reflection of current sensory input. As such, the LDN may serve an important integrative function for limbic spatial learning systems.     

Responses of neurons in primary and inferior temporal visual cortices to natural scenes

The primary visual cortex (V1) is the first cortical area to receive visual input, and inferior temporal (IT) areas are among the last along the ventral visual pathway. We recorded, in area V1 of anaesthetized cats and area IT of awake macaque monkeys, responses of neurons to videos of natural scenes. Responses were analysed to test various hypotheses concerning the nature of neural coding in these two regions. A variety of spike-train statistics were measured including spike-count distributions, interspike interval distributions, coefficients of variation, power spectra, Fano factors and different sparseness measures. All statistics showed non-Poisson characteristics and several revealed self-similarity of the spike trains. Spike-count distributions were approximately exponential in both visual areas for eight different videos and for counting windows ranging from 50 ms to 5 seconds. The results suggest that the neurons maximize their information carrying capacity while maintaining a fixed long-term-average firing rate, or equivalently, minimize their average firing rate for a fixed information carrying capacity.     

Sensory responsiveness of "broad-spike" neurons in the laterodorsal tegmental nucleus, locus coeruleus and dorsal raphe of awake rats: implications for cholinergic and monoaminergic neuron-specific responses

Although cholinergic neurons in the laterodorsal and pedunculopontine tegmental nuclei have been shown to have a pivotal role in neural mechanisms of paradoxical sleep, their function during wakefulness is less understood. To examine the latter, we have recorded from "broad-spike neurons", which were distinguished by their long spike duration, in the laterodorsal tegmental nucleus of undrugged, head-restrained rats, and examined their response properties to sensory stimuli such as light touch to the tail, air puff to the face, 2 kHz pure tone and flashes of light. Broad-spike neurons from the locus coeruleus and dorsal raphe nucleus were studied for comparison; these neurons have been demonstrated to be noradrenergic and serotonergic, respectively. The broad-spike neurons in the laterodorsal tegmental nucleus have also been suggested to be cholinergic. There were two kinds of responses: (1) a simple increase or decrease in firing, reflecting an elevated level of vigilance; and (2) a phasic response composed of a single spike or brief, high frequency burst, usually diminishing or disappearing upon repetition of the stimulus. When two or more types of stimuli were effective in a neuron, they evoked responses of the same quality. Most of the dorsal raphe neurons displayed only the simple increase of firing, whereas the locus coeruleus neurons gave a phasic response with rather weak attenuation upon repetition. Compared with these, the laterodorsal tegmental neurons were heterogeneous: about one-quarter showing only a simple change of firing (half increasing, half decreasing); and two-thirds displaying phasic responses. The latter response of many neurons attenuated strongly upon repetition. The laterodorsal tegmental neurons were classified into several groups according to their spontaneous firing behavior during sleep and wakefulness, but every neuron in a group did not show the same type of response. For example, some of the neurons which were most active during paradoxical sleep and essentially silent during wakefulness decreased or stopped firing upon sensory stimulation, while others in this group had strong phasic responses. These results suggest that putative cholinergic neurons in the laterodorsal tegmental nucleus have heterogenous properties not only with respect to their spontaneous activity during sleep and wakefulness but also with respect to their response to sensory stimulation. Some of these neurons may function to induce a global attentive state in response to a novel stimulus.     

Phasic firing of single neurons in the rat nucleus accumbens correlated with the timing of intravenous cocaine self-administration

To examine potential neural mechanisms involved in cocaine self-administration, the activity of single neurons in the nucleus accumbens of rats was recorded during intravenous cocaine self-administration. Lever pressing was reinforced according to a fixed-ratio 1 schedule. On a time base comparable to the interinfusion interval, half the neurons exhibited phasic firing patterns time locked to the cocaine reinforced level press. For almost all neurons, this pattern consisted of a change in firing rate postpress, typically a decrease, followed by a reversal of that change. The postpress change was closely related to the lever press. Typically, it began within the first 0.2 min postpress and culminated within the first 1.0 min postpress. For a small portion of responsive neurons, the reversal of the postpress change was punctate and occurred within 1-3 min of either the last lever press or the next lever press so that firing was stable during much of the interinfusion interval. For the majority of neurons, the reversal was progressive; it began within 2 min after the previous level press, and it was not complete until the last 0.1-2.0 min before the next lever press. The duration of this progressive reversal, but not of the postpress change, was positively correlated with the interinfusion interval. Thus, in addition to exhibiting changes in firing related to the occurrence of self-infusion, the majority of neurons also exhibited progressive changes in firing related to the spacing of infusions. In a structure that has been shown to be necessary for cocaine self-administration, such a firing pattern is a likely neurophysiological component of the mechanism that transduces declining drug levels into increased drug-related appetitive behavior. It is, thus, a neural mechanism that may contribute to compulsive drug-maintained drug taking.     

Arousal-related associative response characteristics of dorsal lateral geniculate nucleus neurons during acoustic Pavlovian fear conditioning.

This research determined whether fear-conditioned, acoustic stimuli induce thalamic arousal reflected in associative responses in dorsal lateral geniculate nucleus (dLGN) neurons. Rabbits received a Pavlovian discriminative fear conditioning procedure in which one tone conditioned stimulus (CS+) was always paired with an aversive unconditioned stimulus (UCS) and another tone (CS–) was never paired with the UCS. Responses of single dLGN neurons to random CS+ and CS– presentations were then recorded. Nine of 15 recorded neurons demonstrated significantly greater firing during the CS+ versus the CS–. Their spontaneous activity demonstrated tonic firing during increased neocortical arousal and burst firing during decreased neocortical arousal. The results demonstrate that dLGN neurons show associative responses to fear-conditioned, acoustic stimuli and present a model for investigating the neural circuits by which such stimuli affect sensory processing at the thalamic level. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Antidromically identified striatonigral projection neurons in the chronically implanted behaving rat: Relations of cell firing to amphetamine-induced behaviors.

The effects of systemically administered amphetamine (0.25–5.0 mg/kg, sc) on neostriatal neurons recorded in chronically implanted behaving rats were studied. Projection neurons, identified by antidromic activation from the substantia nigra, fired infrequently during most predrug behaviors. Nonantidromic cells also tended to fire slowly. Cells of both type showed up to 10-fold variations in firing rate across behaviors. For most neurons, amphetamine caused a reduction in the firing rate during related pre- and postdrug behaviors. For instance, the firing rate of 28 of 42 neurons was reduced during the initial amphetamine-induced locomotion as compared with the rate during predrug locomotion. Moreover, with the higher doses of amphetamine, there was a further reduction in firing rate corresponding to the transition from locomotion to stereotypies. In contrast to previous studies, results suggest that amphetamine inhibits the numerous slowly firing neostriatal neurons, many of which were identified as projection neurons. Thus amphetamine alters the magnitude and pattern of neostriatal control of its neural targets. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The 5-HT1A receptor antagonist p-MPPI blocks 5-HT1A autoreceptors and increases dorsal raphe unit activity in awake cats

The effects of the putative 5-HT1A receptor antagonist 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzam ide (p-MPPI) were examined on the activity of serotonergic dorsal raphe nucleus neurons in freely moving cats. Systemic administration of p-MPPI produced a dose-dependent increase in firing rate. This stimulatory effect of p-MPPI was evident during wakefulness (when serotonergic neurons display a relatively high level of activity), but not during sleep (when serotonergic neurons display little or no spontaneous activity). p-MPPI also blocked the ability of the 5-HT1A receptor agonist 8-hydroxy-(2-di-n-propylamino)tetralin (8-OH-DPAT) to inhibit serotonergic neuronal activity. This antagonism was evident both as a reversal of the neuronal inhibition produced by prior injection of 8-OH-DPAT and as a shift in the potency of 8-OH-DPAT following p-MPPI pretreatment. Overall, these results in behaving animals indicate that p-MPPI acts as an effective 5-HT1A autoreceptor antagonist. The increase in firing rate produced by p-MPPI supports the hypothesis that autoreceptor-mediated feedback inhibition operates under physiological conditions.     

Context-Dependent Reorganization of Spatial and Movement Representations by Simultaneously Recorded Hippocampal and Striatal Neurons During Performance of Allocentric and Egocentric Tasks.

Hippocampal and striatal place- and movement-correlated cell firing was recorded as rats performed place or response tasks in a familiar environment, and then after cue manipulation. In a familiar environment, place field properties did not differ across brain structures or task conditions. Movement correlates were stronger during place task performance only in hippocampal neurons. After cue manipulations, place- and movement-sensitive hippocampal and striatal neurons changed their correlate strength, regardless of behavioral strategy. Thus, for both structures, place-correlated cells may encode spatial context information, whereas movement-correlated cells may represent both egocentric movement and learned behavioral responses. The striking overall similarity between hippocampal and striatal neural responses to context manipulation (regardless of strategy) suggests that these structures operate continuously, and in parallel, during multiple forms of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Superiority of centrifugal pump over roller pump in paediatric cardiac surgery: prospective randomised trial

The perirhinal cortex (PRC) plays a major role in memory processes. This role may be influenced by activity in the adjacent entorhinal cortex (EC) and hippocampus (HPC), particularly during the processing of spatial information. In the current experiment we sought to determine whether the cholinergically mediated (type II) theta rhythm, which is a prominent electrophysiological feature of both HPC and EC activity, influenced neuronal firing in the PRC of urethane-anesthetized rats. When the spontaneous firing activity of single units recorded in PRC was related to theta recorded from the hippocampal fissure, it was determined that the firing of 50/163 (31%) PRC neurons exhibited a statistically significant phase relationship (mean phase angle = 188 degrees) to HPC theta. Thirty-three (66%) of these neurons tended to fire near the trough, and 17 near the peak, of this activity. These data indicate that a high proportion of PRC neurons participate in hippocampal-entorhinal theta activity. This activity may support information transmission and storage within and between these structures.     

Computer simulation of the enteric neural circuits mediating an ascending reflex: roles of fast and slow excitatory outputs of sensory neurons

Recent electrophysiological studies of the properties of intestinal reflexes and the neurons that mediate them indicate that the intrinsic sensory neurons may transmit to second order neurons via either fast (30-50 ms duration) or slow (10-60 s duration) excitatory synaptic potentials or both. Which of these possible modes of transmission is involved in the initiation of motility reflexes has not been determined and it is not clear and what the consequences of the different forms of synaptic transmission would be for the properties of the reflex pathways. In the present study, this question has been addressed by the use off a suite of computer programs, Plexus, which was written to simulate the activity of the neurons of the enteric nervous system during intestinal reflexes. The programs construct a simulated enteric nerve circuit based on anatomical and physiological data about the number, functions and interconnections of neurons involved in the control of motility. The membrane potentials of neurons are calculated individually from physiological data about the reversal potentials and membrane conductances for Na+, K+ and Cl-. Synaptic potentials are simulated by changes in specific conductances based on physiological data. The results of each simulation are monitored by recording the membrane potentials of up to 16 separate defined neurons and by recording the summed activity of whole classes of neurons as a function of time and location in the stimulated network. The present series of experiments simulated the behaviour of a network consisting of 18,898 sensory neurons and 3708 ascending interneurons after 75% of the sensory neurons lying in the anal 10 mm of a 30 mm long segment of small intestine were stimulated once. The results were compared with electrophysiological data recorded from myenteric neurons during ascending reflexes evoked either by distension or mechanical stimulation of the mucosa. When transmission from sensory neurons to ascending interneurons was via fast excitatory synaptic potentials, the latencies and durations of the simulated responses were too brief to match the electrophysiologically recorded responses. When transmission from sensory neurons was via slow excitatory synaptic potentials, the latencies were very similar to those recorded physiologically, but the durations of the stimulated responses were much longer than seen in physiological experiments. The latencies and durations of simulated and physiologically recorded responses matched only when the firing of ascending interneurons was limited to the beginning of a slow excitatory synaptic (in this study by limiting the duration of the decrease in K+ conductance). The simulation provided several physiologically testable predictions, indicating that Plexus is an important tool for the investigation of the properties and behaviour of the enteric nervous system.