Cortical lateralization of function in rats in a visual reaction time task

Dynamics of electroencephalogram oscillations underlie right-eye preferences in predatory behavior of the music frog

Visual lateralization is a typical characteristic of many vertebrates; however, its underlying dynamic neural mechanism is unclear. In this study, predatory responses and dynamic brain activities were evaluated in the Emei music frog (Nidirana daunchina) to assess the potential eye preferences and their underlying dynamic neural mechanism, using behavioral and electrophysiological experiments, respectively. To do this, when the prey stimulus (live cricket and leaf as control) was moved around the frogs in both clockwise and anticlockwise directions at constant velocity, the number of predatory responses were counted and electroencephalogram (EEG) absolute power spectra for each band were measured for the telencephalon, diencephalon and mesencephalon. The results showed that: (1) no significant differences in the number of predatory responses could be found for the control (leaf), but the number of predatory responses for the right visual field (RVF) was significantly greater than that for the left visual field (LVF) when the live cricket was moved into the RVF clockwise; (2) compared with no stimulus in the visual field and stimulus in the LVF, the power spectra of each EEG band were greater when the prey stimulus was moved into the RVF clockwise; and (3) the power spectra of the theta, alpha and beta bands in the left diencephalon were significantly greater than those of the right counterpart for the clockwise direction, but similar significant differences presented for the delta, theta and alpha bands in the anticlockwise direction. Together, the results suggested that right-eye preferences for predatory behaviors exist in music frogs, and that the dynamics of EEG oscillations might underlie this right eye/left hemisphere advantage.

Searching for inhibition of return in the rat using the covert orienting of attention task

Inhibition of return (IOR) is an important psychological construct describing inhibited responses to previously attended locations. In humans, it is investigated using Posner's cueing paradigm. This paradigm requires central visual fixation and detection of cued stimuli to the left or right of the fixation point. Stimuli can be validly or invalidly cued, appearing in the same or opposite location to the cue. Although a rat version of the spatial cueing paradigm (the covert orienting of attention task) does exist, IOR has so far not been demonstrated. We therefore investigated whether IOR could be robustly demonstrated in adult male rats using the covert orienting of attention task. This task is conducted in holed wall operant chambers with the central three holes mimicking the set-up for Posner cueing. Across four samples of rats (overall n = 84), we manipulated the following task parameters: stimulus onset asynchronies (Experiments 1-3), cue brightness (Experiment 1b) and the presence of a central reorienting event (Experiment 4). In Experiment 1, we also investigated strain differences by comparing Lister Hooded rats to Sprague-Dawley rats. Although Lister Hooded rats briefly showed evidence of IOR (Experiment 1a, and see Online Resource 1 data), we were unable to replicate this finding in our other experiments using different samples of this strain. Taken together, our findings suggest that IOR cannot be robustly demonstrated in the rat using the covert orienting of attention task conducted in holed wall operant chambers.

Attempt-dependent decrease in skilled reaching characterizes the acute postsurgical period following a forelimb motor cortex lesion: an experimental demonstration of learned nonuse in the rat

The notion that shock or diaschisis is a distinctive stage in the recovery process following brain damage has played a formative role in the characterization of brain injury. For example, damage to the forelimb region of motor cortex results in an acute period of behavioural depression in skilled reaching and other skilled actions followed by improved performance mediated by compensatory movements. Whereas the progression of improvement and the use of compensatory movements in the chronic period of recovery is well-documented, temporal aspects of behaviour during the acute period of depression of behaviour are relatively unstudied. The present study examined the temporal scheduling of reach-attempts by rats attempting to gain single pellets of food from a shelf in a skilled reaching task. Pretrained rats received contralateral-to-the-pretrained limb forelimb motor cortex lesions. Control lesions included contralateral-to-the-pretrained limb parietal cortex lesions, or ipsilateral-to-the-pretrained limb motor cortex lesions. Frame-by-frame video analysis of behaviour showed a decrease in reaching attempts as a function of successive approaches and attempts to grasp the food over the first few postsurgical days in rats with contralateral-to-the-pretrained limb motor cortex lesions. A similar approach-dependent decrease in attempts did not occur after parietal or ipsilateral-to-the-pretrained limb motor cortex lesions. The decrease in responding occurred only during acute testing and was not observed in rats first tested after 8 days of postoperative recovery. The findings are discussed in relation to the ideas that: (1) the stroke subject is an active participant in modifying behaviour to cope with injury; (2) learned nonuse contributes to behaviour in the acute postinjury period following motor cortex injury; (3) diaschisis inadequately accounts for poststoke behaviour.

Unilateral lesions of the medial agranular cortex impair responding on a lateralised reaction time task

The present study assessed the behavioural sequalae of unilateral excitotoxic cortical lesions made either in the medial agranular cortex (AGm) or in the medial prefrontal cortex (mPFC) using a visual reaction time task. The task required animals to sustain a nose-poke in a central hole, until a brief light stimulus was presented in either of two holes which were located on the same side of the box: this enabled performance on each side of the rat's body to be assessed independently. Lesions of the AGm impaired performance on the contralateral side, with rats biasing their responding to the nearer of the two response locations. Analysis of the deficit revealed that rats were able to discriminate between the two stimuli and suggested that AGm lesions disrupted the control of contralateral responding. Lesions of the mPFC produced similar response-related deficits, but these were more transient in nature. Neither AGm lesions nor mPFC lesions impaired performance on the ipsilateral side, consistent with the concept of an egocentrically coded deficit.

The Effects of Early Environment on the Development of Functional Laterality in Morris Maze Performance

The current study examined the contribution of early postnatal experience to the functional lateralisation of spatial ability in the male rat. Litters were handled (H) or non-handled (NH) during the first 20 days of life, and three males from each litter were tested in the Morris water maze in adulthood. Two subjects from each litter were monocularly tested, one with the right eye patched and the other with the left eye patched. A third subject in each litter was tested with both eyes open. Handling interacted with Eye Patch for time and distance measures. Performance of Right- and Left-Patched rats was equivalent for the NH group, but the H subjects tested with the Right Patch outperformed H subjects with the Left Patch. These results confirm studies that found spatial navigation performance to be lateralised to the right hemisphere in male rats. The data indicate that functional asymmetry of spatial navigation behaviour in the adult male rat is sensitive to environmental influences during early development.

Visuospatial attention in the rat and posterior parietal cortex lesions

Covert attention to visuospatial stimuli was assessed in rats using a modified version of a task designed for human subjects. Rats were trained to respond toward bright target lights presented to the right or left visual space. Dim cue lights served to attract their attention prior to the onset of the bright target lights. Consistent with previous research using similar paradigms, rats in this experiment displayed longer reaction times during trials in which the cue and target lights were presented on opposite sides of visual space. Throughout pre- and post-operative testing, individual subjects showed lateralized differences in the performance of this task as indicated by asymmetries in reaction time, the percentage of correct responses, and the number of responses made to each side of visual space (response bias). Lesioning the area of cortex thought to be a possible homolog of the posterior parietal cortex in primates produced no specific effects on performance. It is suggested that this paradigm may tap into an evolutionarily conserved attentional process, but that this process may be subserved by somewhat different neural structures in different species.

The effect of kindling of different nuclei in the left and right amygdala on anxiety in the rat

The effects on rodent anxiety of kindling in the medial or basolateral amygdaloid nuclei in each hemisphere were examined. Anxiety was measured using the hole board and elevated plus maze tests. The animals were kindled in medial or basolateral amygdalas, of either the left or right hemisphere. Controls had electrodes implanted in comparable areas, but were not kindled. Analysis of electrode location showed that some animals were kindled in amygdaloid nuclei other than medial or basolateral amygdala. These animals were labelled outliers. Kindling of the medial/basolateral amygdala in the left hemisphere decreased anxiety for at least 1 week after the last kindled seizure. Right hemisphere medial/basolateral kindling tended to increase anxiety. Outlier-kindled rats were less anxious than their controls regardless of hemisphere 1 week after their last kindled seizure. Clear anxiogenic effects were not likely seen in the right hemisphere in this study because of the electrode locations. The degree of anxiety following kindling was correlated with electrode location in the anterior-posterior plane. More anterior foci in the amygdala were associated with more anxiety. More posterior amygdala foci were associated with less anxiety. These findings point to the importance of kindled focus in the amygdala for behavioral effect. Future research should carefully control the location of kindled foci when investigating effects of amygdala kindling on anxiety and other behaviors.

Brain lateralization and immunomodulation

The two sides of the brain may be differently involved in the modulation of immune responses as demonstrated by lesional and behavioral approaches in rodents. Lesions of right or left neocortex induced opposite effects on various immune parameters including mitogen-induced lymphoproliferation, interleukin-2 production, macrophage activation or natural killer cell activity. This animal model, useful to elucidate whereby the brain and the immune system can communicate, appears to be suitable for studying the immune perturbations observed during stroke in humans. Brain asymmetry in modulation of immune reactivity may also be demonstrated in intact animal using a behavioral paradigm. The direction of a lateralized motor behavior ie paw preference in a food reaching task, correlated with an asymmetrical brain organization, was shown to be associated with lymphocyte reactivity, natural killer cell activity and auto-antibody production. The association between paw preference and immune reactivity in mice varies according to the immune parameters tested and is a sex-dependent phenomenon in which genetic background may be involved. The experimental models for investigating asymmetrical brain modulation of the immune system should be useful for studying several physiological, pathological and genetic aspects of neuroimmunomodulation.

Expectancy and stimulus frequency: a comparative analysis in rats and humans

We examined whether expectancy, one of several factors influencing attention, is similarly affected in rats and humans by manipulation of relative stimulus frequency. A two-choice reaction time (RT) task was developed for rats, and an analogous task was used for humans. Errors, RTs, discriminability, and response bias were measured. Both rats and humans shifted their response bias to the more frequent stimulus, with no change in overall discriminability. As stimulus probability or stimulus repetition increased, RTs and errors decreased. These results illustrate the similarity of expectancy in rats and humans. This two-choice RT task for rats can be used in future studies to examine the neuronal mechanisms of expectancy and attention.

Asymmetrical brain modulation of the immune response

It is now well known that the central nervous system can regulate the immune system. Interestingly the two sides of the brain have been demonstrated to be differently involved in the modulation of immune responses. In rodents, lesions of right or left neocortex induced opposite effects on various immune parameters including mitogen-induced lymphoproliferation, interleukin-2 production, macrophage activation or natural killer cell activity. Furthermore in humans, left-handedness has been reported to be associated with a high incidence of immune disorders. Likewise in mice, the direction of a lateralized motor behavior, i.e., paw preference in a food reaching task, correlated with an asymmetrical pattern of brain organization, was shown to be associated with lymphocyte reactivity, natural killer cell activity and auto-antibody production. Conversely the immune system could send to the brain information that may be asymmetrically expressed. The experimental models for investigating asymmetrical brain modulation of the immune system may be useful for studying physiological, pathological and genetic aspects of neuroimmunomodulation.

Effects of unilateral dorsal and ventral striatal dopamine depletion on visual neglect in the rat: a neural and behavioural analysis

Rats were trained in a specially designed apparatus to detect brief, unpredictable visual stimuli presented to either side of the head. In one condition, rats reported the detection of the visual stimulus by removing their heads from a central location and responding in one of two adjacent side-holes where the visual stimulus had occurred. In the other condition, rats were trained to respond in the hole on the opposite side to where the visual stimulus had occurred. Following training all rats received striatal infusions of 6-hydroxydopamine leading to profound striatal dopamine depletion. One group received unilateral intra-nucleus accumbens 6-hydroxydopamine infusions. Two groups received 6-hydroxydopamine unilaterally into the caudate nucleus. Two other groups received two infusions of 6-hydroxydopamine, intra-accumbens and intra-caudate, on either the same side or on opposite sides. The results showed that all groups, except that receiving only intra-accumbens 6-hydroxydopamine, exhibited a significant bias in responding towards the side of the lesion which correlated with dopamine depletion in the head of the caudate nucleus, regardless of the type of discrimination or pre-operative strategy. These biased groups were also slower to initiate, but not to complete, contralateral responses. Detailed analysis of the behavioural evidence suggested that unilateral striatal dopamine depletion does not produce sensory loss or sensory inattention but rather an output type neglect, perhaps related to hemiakinesia or "intentional neglect". The bias recovered to preoperative levels by 7 weeks after surgery, but could be reinstated by pretreatment with alpha-methyl-para-tyrosine, thus suggesting the involvement of presynaptic mechanisms in recovery. Although unilateral dopamine depletion from the nucleus accumbens alone had no effects on visual neglect, it produced a lateralized bias in premature responding away from the side of the lesion, contrasting with the bias towards the side of the lesion seen in all of the other groups. These effects appeared to summate in this and in another condition in which a more eccentric response was required for stimulus detection, to suggest an interaction in function between the dorsal and ventral striatum.