Left-right asymmetry in firing rate of extra-retinal photosensitive neurons in the crayfish.

The purpose of this paper is to explore the firing rate of the caudal photoreceptors (CPRs) from the sixth abdominal ganglion of the crayfish Cherax quadricarinatus. We use simultaneous extracellular recordings on left and right CPR in the isolated ganglion (n = 10). The CPRs showed an asymmetry in the spontaneous activity and light-induced response. In darkness, we observed one subgroup (70%) in which the left CPR (CPR-L) and right CPR (CPR-R) had spontaneous firing rates with a median of 18 impulses/s and 6 impulses/s, respectively. In another subgroup (20%), the CPR-R had a median of 15 impulses/s and the CPR-L had 8 impulses/s. In both groups, the differences were significant. Furthermore, the CPRs showed an asymmetrical photoresponse induced by a pulse of white light (700 Lux, 4 s). In one subgroup (30%), the CPR-L showed light-induced activity with a median of 73%, (interquartile range, IQR = 51), while the CPR-R had a median of 41%, (IQR = 47). In another subgroup (70%), the CPR-R showed a median of 56%, (IQR = 51) and the CPR-L had a median of 42%, (IQR = 46). In both groups, the differences were significant. Moreover, we observed a differential effect of temperature on CPR activity. These results suggest a functional asymmetry in both activities from left and right CPRs. These CPR activity fluctuations may modulate the processing of information by the nervous system.

The effect of unilateral disruption of the centrifugal visual system on normal eye development in chicks raised under constant light conditions.

The centrifugal visual system (CVS) comprises a visually driven isthmic feedback projection to the retina. While its function has remained elusive, we have previously shown that, under otherwise normal conditions, unilateral disconnection of centrifugal neurons in the chick affected eye development, inducing a reduced rate of axial elongation that resulted in a unilateral hyperopia in the eye contralateral to the lesion. Here, we further investigate the role of centrifugal neurons in ocular development in chicks reared in an abnormal visual environment, namely constant light. The baseline ocular phenotype of constant light-reared chicks (n = 8) with intact centrifugal neurons was assessed over a 3-week post-hatch time period and, subsequently, compared to chicks raised in normal diurnal lighting (n = 8). Lesions of the isthmo-optic tract or sham surgeries were performed in another seventeen chicks, all raised under constant light. Ocular phenotyping was performed over a 21-day postoperative period to assess changes in refractive state (streak retinoscopy) and ocular component dimensions (A-scan ultrasonography). A pathway-tracing paradigm was employed to quantify lesion success. Chicks raised in constant light conditions with an intact CVS developed shallower anterior chambers combined with elongated vitreous chambers relative to chicks raised in normal diurnal lighting. Seven days following surgery to disrupt centrifugal neurons, a significant positive correlation between refractive error asymmetry between the eyes and lesion success was evident, characterized by hyperopia in the eye contralateral to the lesion. By 21 days post-surgery, these contralateral eyes had become emmetropic, while ipsilateral eyes had developed relative axial hyperopia. Our results provide further support for the hypothesis that the centrifugal visual system can modulate eye development.

18F-FDG PET/TC y RM funcional en un caso de afasia progresiva primaria logopénica cruzada / 18F-FDG PET/CT and functional MRI in a case of crossed logopenic primary progressive aphasia

La afasia progresiva primaria es un síndrome clínico secundario a la neurodegeneración de las áreas y redes neuronales involucradas en el lenguaje, habitualmente en el hemisferio izquierdo. El término «afasia cruzada» se refiere a una alteración del lenguaje como consecuencia de una lesión del hemisferio cerebral ipsilateral a la mano dominante. Presentamos el caso de una mujer diestra de 75 años con afasia progresiva primaria logopénica, con dificultad para encontrar palabras, de 2 años de evolución. La 18F-FDG PET/TC mostró un hipometabolismo temporoparietal derecho. Se realizó una RM funcional para caracterizar patrones de lateralización del lenguaje. Se observó un patrón de activación similar en ambos hemisferios y una menor activación de la esperada en el giro frontal inferior bilateral. Estos hallazgos apoyan que la afasia progresiva primaria logopénica no debería considerarse como una afectación de inicio en el hemisferio izquierdo, sino un síndrome caracterizado por una neurodegeneración asimétrica con preferencia por áreas y redes neuronales implicadas en el lenguaje (AU)

Primary progressive aphasia is a clinical syndrome caused by a neurodegeneration of areas and neural networks involved in language, usually in the left hemisphere. The term "crossed aphasia" denotes an acquired language dysfunction caused by a lesion in the hemisphere ipsilateral to the dominant hand. A case is presented on a 75-year-old right-handed woman with a logopenic variant of primary progressive aphasia with word-finding difficulties of 2 years onset. The 18F-FDG PET/CT showed right temporoparietal hypometabolism. A functional MRI scan was performed during a verb naming task in order to characterise language lateralisation patterns. A similar activation pattern was observed in both hemispheres, with less activation than expected in bilateral inferior frontal gyrus. These findings support that logopenic variant of primary progressive aphasia should not be considered as a neurodegeneration starting in the left brain hemisphere, but as a syndrome characterised by asymmetric neurodegeneration of brain regions and neural networks involved in language (AU)

Red LED photobiomodulation reduces pain hypersensitivity and improves sensorimotor function following mild T10 hemicontusion spinal cord injury.

BACKGROUND: The development of hypersensitivity following spinal cord injury can result in incurable persistent neuropathic pain. Our objective was to examine the effect of red light therapy on the development of hypersensitivity and sensorimotor function, as well as on microglia/macrophage subpopulations following spinal cord injury. METHODS: Wistar rats were treated (or sham treated) daily for 30 min with an LED red (670 nm) light source (35 mW/cm(2)), transcutaneously applied to the dorsal surface, following a mild T10 hemicontusion injury (or sham injury). The development of hypersensitivity was assessed and sensorimotor function established using locomotor recovery and electrophysiology of dorsal column pathways. Immunohistochemistry and TUNEL were performed to examine cellular changes in the spinal cord. RESULTS: We demonstrate that red light penetrates through the entire rat spinal cord and significantly reduces signs of hypersensitivity following a mild T10 hemicontusion spinal cord injury. This is accompanied with improved dorsal column pathway functional integrity and locomotor recovery. The functional improvements were preceded by a significant reduction of dying (TUNEL(+)) cells and activated microglia/macrophages (ED1(+)) in the spinal cord. The remaining activated microglia/macrophages were predominantly of the anti-inflammatory/wound-healing subpopulation (Arginase1(+)ED1(+)) which were expressed early, and up to sevenfold greater than that found in sham-treated animals. CONCLUSIONS: These findings demonstrate that a simple yet inexpensive treatment regime of red light reduces the development of hypersensitivity along with sensorimotor improvements following spinal cord injury and may therefore offer new hope for a currently treatment-resistant pain condition.

Haptic recognition of familiar objects: examining lateralization of specificity effects.

Previous research has found evidence in favor of two subsystems underlying object recognition: an abstract-category subsystem that mainly works in the left hemisphere (LH) and a specific-exemplar subsystem that mainly works in the right hemisphere (RH). This asymmetry has been observed in both the visual and auditory domains by means of long-term repetition priming experiments. This study explored whether this asymmetrical pattern extends to the haptic domain through an experiment in which 30 right-handed participants (24 women) ages 18 to 38 years could identify familiar objects with a single hand. The procedure included two blocks of trials, the study (presentation of primes) and the test phase (presentation of targets), separated by a short distractor task. Of interest was if repetition of the same exemplar object (e.g., the same cigarette lighter) produced more priming than repetition of a different exemplar of the same object category (e.g., a different cigarette lighter), and, crucially, if this hypothetical same-exemplar advantage (specificity) was larger when objects were identified with the left hand (RH). An ANOVA was performed on RTs with priming type (same-exemplar primed, different-exemplar primed and unprimed) and hand (left, right) as within-participants factors. Results showed a main effect of priming type due to a same-exemplar advantage (shorter RTs) both for the left and the right hand, but a non-significant interaction between specificity effects and hands.

Lateralization of activity in the parietal cortex predicts the effectiveness of bilateral transcranial direct current stimulation on performance of a mental calculation task.

Transcranial direct current stimulation (tDCS) is a non-invasive technique that moderates cognitive and motor function. The effects of tDCS on cognitive and motor tasks vary among individuals. However, the source of the inter-individual variability remains unknown. The purpose of the present study was to examine whether the effect of bilateral tDCS on the performance of mental calculations differs among individuals according to the functional lateralization of parietal activity observed during a mental calculation task. Sixteen healthy subjects (11 males and five females, aged 20-23 years) participated. Laterality of parietal activity during a mental calculation task was evaluated using functional magnetic resonance imaging. Subjects also performed the mental calculation task pre-, during-, 30 min post-, and 60 min post-tDCS. Bilateral tDCS with the anode over the left parietal cortex and the cathode over the right parietal cortex shortened response times of the mental calculation task in subjects with left-hemispheric parietal lateralization, but not in subjects with bilateral parietal activation. This indicates that inter-individual variability in laterality of brain activity might be an important factor underlying the effect of bilateral tDCS. In conclusion, bilateral tDCS over the parietal cortex enhanced the performance of mental calculations in subjects with left-hemispheric parietal lateralization.

The neurobiology of rhyme judgment by deaf and hearing adults: an ERP study.

We used electrophysiology to determine the time course and distribution of neural activation during an English word rhyme task in hearing and congenitally deaf adults. Behavioral performance by hearing participants was at ceiling and their ERP data replicated two robust effects repeatedly observed in the literature. First, a sustained negativity, termed the contingent negative variation, was elicited following the first stimulus word. This negativity was asymmetric, being more negative over the left than right sites. The second effect we replicated in hearing participants was an enhanced negativity (N450) to nonrhyming second stimulus words. This was largest over medial, parietal regions of the right hemisphere. Accuracy on the rhyme task by the deaf group as a whole was above chance level, yet significantly poorer than hearing participants. We examined only ERP data from deaf participants who performed the task above chance level (n = 9). We observed indications of subtle differences in ERP responses between deaf and hearing groups. However, overall the patterns in the deaf group were very similar to that in the hearing group. Deaf participants, just as hearing participants, showed greater negativity to nonrhyming than rhyming words. Furthermore the onset latency of this effect was the same as that observed in hearing participants. Overall, the neural processes supporting explicit phonological judgments are very similar in deaf and hearing people, despite differences in the modality of spoken language experience. This supports the suggestion that phonological processing is to a large degree amodal or supramodal.

Left lateralizing transcranial direct current stimulation improves reading efficiency.

BACKGROUND: Poor reading efficiency is the most persistent problem for adults with developmental dyslexia. Previous research has demonstrated a relationship between left posterior temporal cortex (pTC) function and reading ability, regardless of dyslexia status. OBJECTIVE/HYPOTHESIS: In this study, we tested whether enhancing left lateralization of pTC using transcranial direct current stimulation (tDCS) improves reading efficiency in adults without dyslexia. METHOD: Twenty-five right-handed adults with no history of learning disorder participated. Real and sham "Left lateralizing" tDCS were applied to the pTC in separate sessions. Standardized word and nonword reading tests were given immediately after stimulation. RESULTS: Modeling of the induced electrical field confirmed that tDCS was likely to increase left pTC excitability and reduce right pTC excitability as intended. Relative to sham, real tDCS induced improvements in word reading efficiency in below average readers. CONCLUSIONS: Enhancing left lateralization of the pTC using tDCS improves word reading efficiency in below-average readers. This demonstrates that left lateralization of the pTC plays a role in reading ability, and provides stimulation parameters that could be used for a trial of tDCS in adults with developmental dyslexia. Such short-term gains could amplify the effect of appropriate reading interventions when performed in conjunction with them.

Head tilt in rats during exposure to a high magnetic field.

During exposure to high strength static magnetic fields, humans report vestibular symptoms such as vertigo, apparent motion, and nausea. Rodents also show signs of vestibular perturbation after magnetic field exposure at 7 tesla (T) and above, such as locomotor circling, activation of vestibular nuclei, and acquisition of conditioned taste aversions. We hypothesized that the acute effects of the magnetic field might be seen as changes in head position during exposure within the magnet. Using a yoked restraint tube that allowed movement of the head and neck, we found that rats showed an immediate and persistent deviation of the head during exposure to a static 14.1 T magnetic field. The direction of the head tilt was dependent on the orientation of the rat in the magnetic field (B), such that rats oriented head-up (snout towards B+) showed a rightward tilt of the head, while rats oriented head-down (snout towards B-) showed a leftward tilt of the head. The tilt of the head during magnet exposure was opposite to the direction of locomotor circling immediately after exposure observed previously. Rats exposed in the yoked restraint tube showed significantly more locomotor circling compared to rats exposed with the head restrained. There was little difference in CTA magnitude or extinction rate, however. The deviation of the head was seen when the rats were motionless within the homogenous static field; movement through the field or exposure to the steep gradients of the field was not necessary to elicit the apparent vestibulo-collic reflex.

Noninvasive transorbital alternating current stimulation improves subjective visual functioning and vision-related quality of life in optic neuropathy.

BACKGROUND: Noninvasive repetitive transorbital alternating current stimulation (rtACS) can improve visual field size in patients with optic nerve damage, but it is not known if this is of subjective relevance. We now assessed patient reported outcomes to determine the association between visual field changes and vision-related quality of life (QoL). METHODS: Patients having visual field impairments long after optic nerve damage (mean lesion age 5.5 years) were randomly assigned to a rtACS (n = 24) or sham stimulation group (n = 18). Visual fields and patient reported outcome measures (vision-related QoL: National Eye Institute Visual Function Questionnaire, NEI-VFQ and health-related QoL: Short Form Health Survey, SF-36) were collected before and after a 10-day treatment course with daily sessions of 20 to 40 minutes. The primary outcome measure was the percent change from baseline of detection ability (DA) in defective visual field sectors as defined by computer-based high resolution perimetry (HRP). Secondary outcome parameters included further HRP parameters as well as static and kinetic perimetry results. Changes in QoL measures were correlated with changes in primary and secondary outcome measures in both groups. RESULTS: DA increase in the defective visual field was significantly larger after rtACS (41.1 ± 78.9%, M ± SD) than after sham stimulation (13.6 ± 26.3%), P < 0.05. While there was a significant increase of DA in the whole tested HRP visual field after rtACS (26.8 ± 76.7%, P < 0.05), DA in sham-stimulation patients remained largely unchanged (2.7 ± 20.2%, ns). Results of secondary outcome measures (static and kinetic perimetry) provided further evidence of rtACS efficacy. Improvements in NEI-VFQ subscale "general vision" were observed in both groups but were larger in the rtACS group (11.3 ± 13.5, Z = -3.21, P < 0.001) than in the sham group (4.2 ± 9.4, Z = -1.73, P < 0.05) with a significant difference between groups (Z = -1.71, P < 0.05). DA change and some NEI-VFQ domains were correlated (r = 0.29, P < 0.05), but no significant correlations were observed between DA and SF-36 results. CONCLUSIONS: rtACS facilitates vision restoration after unilateral, long-term optic nerve lesion as assessed both by objective DA changes and improvements in some NEI-VFQ subscales. Both were positively but low correlated, which suggests that factors other than visual field size also contribute to improved vision-related QoL.

Neurobiological responses to stereotactic focal irradiation of the adult rodent hippocampus.

Radiation effectively treats brain tumors and other pathologies but dose and treatment plans are limited by normal tissue injury, a major cause of morbidity in survivors. Clinically significant normal tissue injury can occur even with therapies that target pathological tissue and limit out-of-target irradiation. Elucidating the mechanisms underlying normal tissue injury is facilitated by studying the effects of focal irradiation and comparing irradiated and un-irradiated tissue in experimental animals. Young adult rats were irradiated using the Leksell Gamma Knife® with a 10 Gy maximum dose directed at the left hippocampus and shaped to minimize irradiation contralaterally. At least 95% of targeted hippocampus received ≥3 Gy, while all points in the contralateral hippocampus received <0.3 Gy. Neuronal and microglial markers of damage were assessed in the targeted and contralateral hemispheres of Gamma Knife®-treated rats and compared to non-irradiated controls. Acute cell death and sustained changes in neurogenesis and in microglia occurred in the dentate gyrus of the targeted, but not the contralateral, hippocampus, providing experimental evidence that focal irradiation at doses received by peri-target regions during targeted radiation therapy produces robust normal tissue responses. Additional studies using this approach will facilitate assessment of in vivo dose responses and the cellular and molecular mechanisms of radiation-induced brain injury.

Lateralization of magnetic compass orientation in pigeons.

The aim of our study was to test for lateralization of magnetic compass orientation in pigeons. Having shown that pigeons are capable of learning magnetic compass directions in an operant task, we wanted to know whether the brain hemispheres contribute differently and how the lateralization pattern relates to findings in other avian species. Birds that had learnt to locate food in an operant chamber by means of magnetic directions were tested for lateralization of magnetic compass orientation by temporarily covering one eye. Successful orientation occurred under all conditions of viewing. Thus, pigeons can perceive and process magnetic compass directions with the right eye and left brain hemisphere as well as the left eye and right brain hemisphere. However, while the right brain hemisphere tended to confuse the learned direction with its opposite (axial response), the left brain hemisphere specifically preferred the correct direction. Our findings demonstrate bilateral processing of magnetic information, but also suggest qualitative differences in how the left and the right brain deal with magnetic cues.

Night-migratory garden warblers can orient with their magnetic compass using the left, the right or both eyes.

Several studies have suggested that the magnetic compass of birds is located only in the right eye. However, here we show that night-migrating garden warblers (Sylvia borin) are able to perform magnetic compass orientation with both eyes open, with only the left eye open and with only the right eye open. We did not observe any clear lateralization of magnetic compass orientation behaviour in this migratory songbird, and, therefore, it seems that the suggested all-or-none lateralization of magnetic compass orientation towards the right eye only cannot be generalized to all birds, and that the answer to the question of whether magnetic compass orientation in birds is lateralized is probably not as simple as suggested previously.

Pairwise comparisons and visual perceptions of equal area polygons.

The number of studies related to visual perception has been plentiful in recent years. Participants rated the areas of five randomly generated shapes of equal area, using a reference unit area that was displayed together with the shapes. Respondents were 179 university students from Canada and Poland. The average error estimated by respondents using the unit square was 25.75%. The error was substantially decreased to 5.51% when the shapes were compared to one another in pairs. This gain of 20.24% for this two-dimensional experiment was substantially better than the 11.78% gain reported in the previous one-dimensional experiments. This is the first statistically sound two-dimensional experiment demonstrating that pairwise comparisons improve accuracy.

Red light facilitates the sensed presence elicited by application of weak, burst-firing magnetic fields over the temporal lobes.

To test the hypothesis that the wavelength (color) of ambient lightning should modulate experiences of a sensed presence when the right hemisphere was stimulated by weak, burst-firing magnetic fields, volunteers were exposed for 30 min to this condition or to a sham field while they sat (eyes opened) in either dim red, green, or white light. Subjects exposed to the magnetic field reported significantly more visual sensations along the left side in red light and along the right side in green light. The significant interaction between ambient color and the field treatment was due to the marked increase in experiences of dizziness, sensed presence, "ego-alien" thoughts, and detachment from the body and "being somewhere else" for subjects exposed to the magnetic field while sitting in red light. The concurrence of entoptic images experienced within the upper left peripheral visual field and the sensed presence supported the hypothesis that both are associated with the intrusion of right hemispheric processes into left hemispheric awareness.

Stimulus intensity dependence of cerebral blood volume changes in left frontal lobe by low-frequency rTMS to right frontal lobe: A near-infrared spectroscopy study.

Repetitive transcranial magnetic stimulation (rTMS) has recently been widely employed for the investigation of brain function and treatment of psychiatric and neurological disorders. Although high and low stimulation frequencies are assumed to activate and deactivate brain function, respectively, the optimal parameters of rTMS for treatment of depression have been determined only on the basis of their clinical efficacy. In this study, we administered a 60-s low-frequency rTMS of three grades low intensities over the right dorsolateral prefrontal cortex (DLPFC) in 10 healthy volunteers, and monitored functional changes of the contralateral DLPFC by near-infrared spectroscopy (NIRS) during and immediately after rTMS. Obtained results demonstrated significant [oxy-Hb] decreases during rTMS, and significant differences in the time courses of [oxy-Hb] changes among three stimulus intensities, that is, [oxy-Hb] decreases were most prominent during the latter half of the stimulation and the first 30s of poststimulation only at 15mm condition (58% intensity). These results suggest that monitoring of brain functional changes due to rTMS using NIRS is useful for elucidating the brain mechanisms underlying the clinical effects of rTMS, and the effects of rTMS over contralateral DLPFC are obtained if the stimulus intensities are more than one-half of the motor thresholds.

Interhemispheric transfer of phosphenes generated by occipital versus parietal transcranial magnetic stimulation.

Phosphenes represent a perceptual effect of transcranial magnetic stimulation (TMS) or electric stimulation of visual cortical areas. One likely neural basis for the generation of static phosphenes is the primary visual cortex (V1) although evidence is controversial. A peculiar feature of V1 is that it has sparse callosal connections with the exception of a central portion of visual field representation. In contrast, visually responsive cortical areas in the parietal lobe have widespread callosal connections. Thus, interhemispheric transfer (IT) time of off-centre phosphenes should be slower when generated by V1 than by visual parietal areas. To verify this possibility, in Exp. 1 we measured IT of phosphenes generated by TMS applied to V1 and in Exp. 2 we measured IT of phosphenes obtained by TMS applied to posterior parietal cortex. In both experiments, we obtained static bright circular phosphenes appearing in the contralateral hemifield. We measured IT time behaviorally by comparing unimanual simple reaction time to the onset of a phosphene under crossed or uncrossed hemifield-hand condition (Poffenberger paradigm). In keeping with our prediction, we found a substantially longer IT time for V1 than for parietal phosphenes. Additionally, an IT similar to that obtained with V1 stimulation was found when participants were asked to imagine the phosphenes previously experienced during TMS. In conclusion, the present results suggest that IT of phosphenes either generated by V1 TMS or imagined is subserved by slower callosal channels than those of real visual stimuli or parietal phosphenes.

Light during embryonic development modulates patterns of lateralization strongly and similarly in both zebrafish and chick.

Some aspects of lateralization are widespread. This is clear for the association between left-eye (LE) use and readiness to respond intensely to releasing stimuli presented by others, which has been found in representatives of all major groups of tetrapods and in fishes. In the chick, this behavioural asymmetry is linked developmentally to greater ability to sustain response against distracting stimuli with right-eye (RE) use, in that both reverse with the reversal of the normal RE exposure to light. In the zebrafish, the same two asymmetries (normally) have similar associations with the LE and the RE, and both also reverse together (owing to epithalamic reversal). Here, we show that light exposure early in development is needed in zebrafish to generate both asymmetries. Dark development largely abolishes both the enhanced abilities, confirming their linkage. Resemblance to the chick is increased by the survival in the chick, after dark development, of higher ability to assess familiarity of complex stimuli when using the LE. A somewhat similar ability survives in dark-developed zebrafish. Here, LE use causes lesser reliance on a single recent experience than on longer term past experience in the assessment of novelty. Such resemblances between a fish and a bird suggest that we should look not only for resemblances between different groups of vertebrates in the most common overall pattern of lateralization, but also for possible resemblances in the nature of inter-individual variation and in the way in which it is generated during development.

Muscle-specific variations in use-dependent crossed-facilitation of corticospinal pathways mediated by transcranial direct current (DC) stimulation.

The tendency for contractions of muscles in the upper limb to give rise to increases in the excitability of corticospinal projections to the homologous muscles of the opposite limb is well known. Although the suppression of this tendency is integral to tasks of daily living, its exploitation may prove to be critical in the rehabilitation of acquired hemiplegias. Transcranial direct current (DC) stimulation induces changes in cortical excitability that outlast the period of application. We present evidence that changes in the reactivity of the corticospinal pathway induced by DC stimulation of the motor cortex interact systematically with those brought about by contraction of the muscles of the ipsilateral limb. During the application of flexion torques (up to 50% of maximum) applied at the left wrist, motor evoked potentials (MEPs) were evoked in the quiescent muscles of the right arm by magnetic stimulation of the left motor cortex (M1). The MEPs were obtained prior to and following 10 min of anodal, cathodal or sham DC stimulation of left M1. Cathodal stimulation counteracted increases in the crossed-facilitation of projections to the (right) wrist flexors that otherwise occurred as a result of repeated flexion contractions at the left wrist. In addition, cathodal stimulation markedly decreased the excitability of corticospinal projections to the wrist extensors of the right limb. Thus changes in corticospinal excitability induced by DC stimulation can be shaped (i.e. differentiated by muscle group) by focal contractions of muscles in the limb ipsilateral to the site of stimulation.