RESUMO

Akinetopsia is a rare neurological syndrome characterized by an impaired perception of movement, often resulting from brain damage due to ischemia, epilepsy, or medication. It is also known as visual motion blindness, and patients with this condition are unable to perceive motion normally even with perfect visual acuity. This report aims to present a case of a patient in their late 40 s who developed akinetopsia and also an impairment in movement perception of objects without emitting sounds, after experiencing a late relapse of breast cancer with the occurrence of multiple brain metastases. The patient also experienced visual hallucinations, night terrors, and difficulty forming anterograde memory. Neuroimaging with MRI revealed severe brain damage, especially in the middle temporal area of the visual cortex. Akinetopsia is a rare phenomenon, and this is the first known case of its association with brain metastases.

Assuntos

Neoplasias Encefálicas , Neoplasias da Mama , Humanos , Feminino , Neoplasias Encefálicas/secundário , Neoplasias Encefálicas/complicações , Neoplasias da Mama/patologia , Neoplasias da Mama/complicações , Pessoa de Meia-Idade , Percepção de Movimento/fisiologia , Imageamento por Ressonância Magnética

RESUMO

Serotonergic neurons constitute one of the main systems of neuromodulators, whose diffuse projections regulate the functions of the cerebral cortex. Serotonin (5-HT) is known to play a crucial role in the differential modulation of cortical activity related to behavioral contexts. Some features of the 5-HT signaling organization suggest its possible participation as a modulator of activity-dependent synaptic changes during the critical period of the primary visual cortex (V1). Cells of the serotonergic system are among the first neurons to differentiate and operate. During postnatal development, ramifications from raphe nuclei become massively distributed in the visual cortical area, remarkably increasing the availability of 5-HT for the regulation of excitatory and inhibitory synaptic activity. A substantial amount of evidence has demonstrated that synaptic plasticity at pyramidal neurons of the superficial layers of V1 critically depends on a fine regulation of the balance between excitation and inhibition (E/I). 5-HT could therefore play an important role in controlling this balance, providing the appropriate excitability conditions that favor synaptic modifications. In order to explore this possibility, the present work used in vitro intracellular electrophysiological recording techniques to study the effects of 5-HT on the E/I balance of V1 layer 2/3 neurons, during the critical period. Serotonergic action on the E/I balance has been analyzed on spontaneous activity, evoked synaptic responses, and long-term depression (LTD). Our results pointed out that the predominant action of 5-HT implies a reduction in the E/I balance. 5-HT promoted LTD at excitatory synapses while blocking it at inhibitory synaptic sites, thus shifting the Hebbian alterations of synaptic strength towards lower levels of E/I balance.

Assuntos

Córtex Cerebral , Serotonina , Período Crítico Psicológico , Plasticidade Neuronal , Neurônios Serotoninérgicos

RESUMO

The plasticity of the central nervous system (CNS) allows the change of neuronal organization and function after environmental stimuli or adaptation after sensory deprivation. The so-called critical period (CP) for neuroplasticity is the time window when each sensory brain region is more sensitive to changes and adaptations. This time window is usually different for each primary sensory area: somatosensory (S1), visual (V1), and auditory (A1). Several intrinsic mechanisms are also involved in the start and end of the CP for neuroplasticity; however, which is its duration in S1, VI, and A1? This systematic review evaluated studies on the determination of these time windows in small rodents. The careful study selection and methodological quality assessment indicated that the CP for neuroplasticity is different among the sensory areas, and the brain maps are influenced by environmental stimuli. Moreover, there is an overlap between the time windows of some sensory areas. Finally, the time window duration of the CP for neuroplasticity is predominant in S1.

RESUMO

Scene analysis in video sequences is a complex task for a computer vision system. Several schemes have been addressed in this analysis, such as deep learning networks or traditional image processing methods. However, these methods require thorough training or manual adjustment of parameters to achieve accurate results. Therefore, it is necessary to develop novel methods to analyze the scenario information in video sequences. For this reason, this paper proposes a method for object segmentation in video sequences inspired by the structural layers of the visual cortex. The method is called Neuro-Inspired Object Segmentation, SegNI. SegNI has a hierarchical architecture that analyzes object features such as edges, color, and motion to generate regions that represent the objects in the scenario. The results obtained with the Video Segmentation Benchmark VSB100 dataset demonstrate that SegNI can adapt automatically to videos with scenarios that have different nature, composition, and different types of objects. Also, SegNI adapts its processing to new scenario conditions without training, which is a significant advantage over deep learning networks.

Assuntos

Algoritmos , Córtex Visual , Inteligência Artificial , Humanos , Processamento de Imagem Assistida por Computador , Movimento (Física)

RESUMO

Mercury (Hg) is an environmental contaminant that poses great risk to human health. However, it is still widely used in artisanal gold-mining enterprises around the world, especially in developing countries. Methylmercury (MeHg) is produced environmentally by biomethylation of inorganic Hg present in water sediments, leading to its subsequent accumulation in the aquatic food chain. Due to its high metabolic rate, the Central Nervous System (CNS) is one of the main targets of MeHg. In the present study, we investigate the impact of chronic MeHg intoxication on NADPH diaphorase (NADPH-d) activity and astrocyte mobilization in the visual cortex of the rat. After 60 days of MeHg administration by oral gavage (0.04 mg/kg/day), tissue samples containing the visual cortex were submitted to measurements of Hg levels, NADPH-d activity, and GFAP immunohistochemistry for identification of astrocytes. MeHg intoxication was associated with increased Hg deposits and with reduced NADPH-d neuropil reactivity in the visual cortex. A morphometric analysis suggested that NADPH-d-positive neurons were mostly spared from MeHg harmful action and intoxicated animals had astrocytic activation similar to the control group. The decrease in NADPH-d neuropil reactivity may be due to the negative effect of chronic MeHg poisoning on both the synthesis and transport of this enzyme in afferent pathways to the visual cortex. The relative resistance of NADPH-d-reactive neurons to chronic MeHg intoxication may be associated with peculiarities in cell metabolism or to a protective role of nitric oxide, safeguarding those neurons from Hg deleterious effects.

Assuntos

Astrócitos/efeitos dos fármacos , Poluentes Ambientais/toxicidade , Compostos de Metilmercúrio/toxicidade , NADPH Desidrogenase/metabolismo , Neurônios/efeitos dos fármacos , Córtex Visual/efeitos dos fármacos , Animais , Astrócitos/enzimologia , Comportamento Animal/efeitos dos fármacos , Poluentes Ambientais/metabolismo , Ouro , Humanos , Masculino , Compostos de Metilmercúrio/metabolismo , Mineração , Neurônios/enzimologia , Ratos , Ratos Wistar , Córtex Visual/enzimologia , Córtex Visual/patologia

RESUMO

Single-cell recordings in the primary visual cortex (V1) show neurons with spatial frequency (SF) tuning, which had different responses to chromatic and luminance stimuli. Visually evoked cortical potential (VECP) investigations have reported different spatial profiles. The current study aimed to investigate the spatial selectivity of V1 to simultaneous stimulus of chromatic and luminance contrasts. Compound stimuli temporally driven by m-sequences at 8 SFs were utilized to generate VECP records from thirty subjects (14 trichromats and 16 colorblind subjects). We extracted the second-order kernel, first and second slices (K2.1 and K2.2, respectively). Optimal SF, SF bandwidth, and high SF cut-off were estimated from the best-fitted functions to the VECP amplitude vs SF. For trichromats, K2.1 waveforms had a negative component (N1 K2.1) at 100 ms followed by a positive component (P1 K2.1). K2.2 waveforms also had a negative component (N1 K2.2) at 100 ms followed by a positive deflection (P1 K2.2). SF tuning of N1 K2.1 and N1 K2.2 had a band-pass profile, while the P1 K2.1 was low-pass tuned. P1 K2.1 optimal SF differed significantly from both other negative responses and from P1 K2.2. We found differences in the optimal SF, SF tuning and high SF cut-off among the VECP components. Dichromats had little or no response for all stimulus conditions. The absence of the responses in dichromats, the similarity between the high SF cut-off of the pseudorandom VECPs and psychophysical chromatic visual acuity, and presence of multiple SF tunings suggested that pseudorandom VECPs represented the activity of cells that responded preferentially to the chromatic component of the compound stimuli.

Assuntos

Percepção de Cores/fisiologia , Potenciais Evocados Visuais/fisiologia , Córtex Visual/fisiologia , Vias Visuais/fisiologia , Humanos , Estimulação Luminosa

RESUMO

PURPOSE: To demonstrate that lesions of the visual pathways due to suprasellar tumors are accompanied by alterations of the visual cortex and to see if these alterations are reversible after treatment of tumors by gamma knife radiosurgery. MATERIALS AND METHODS: In 36 patients with peri-optic tumors and defects of their visual fields and in an age-matched control group, magnetic resonance imaging was performed before and after treatment. T1 weighted images were evaluated by voxel-based morphometry and correlated to the degree of visual field defects. RESULTS: In patients, grey matter density and cortical thickness were reduced in all parts of the occipital cortex, reaching significance (p < 0.05) in the left superior and middle occipital gyri, with correlation to visual field defects. Follow-up scans showed further reduction in all occipital areas. CONCLUSION: As in other peripheral lesions of the optic system, damage of the optic pathways affects the visual cortex. A prospective follow-up study is needed to determine if these alterations are reversible after successful tumor treatment.

Assuntos

Adaptação Fisiológica , Neoplasias Encefálicas/diagnóstico por imagem , Neoplasias Encefálicas/radioterapia , Plasticidade Neuronal , Radiocirurgia , Córtex Visual/diagnóstico por imagem , Adolescente , Adulto , Idoso , Neoplasias Encefálicas/fisiopatologia , Criança , Feminino , Seguimentos , Humanos , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Tamanho do Órgão , Estudos Retrospectivos , Resultado do Tratamento , Transtornos da Visão/diagnóstico por imagem , Transtornos da Visão/etiologia , Transtornos da Visão/fisiopatologia , Córtex Visual/fisiopatologia , Campos Visuais/fisiologia , Vias Visuais/diagnóstico por imagem , Vias Visuais/fisiopatologia , Adulto Jovem

RESUMO

PURPOSE: Visual evoked cortical potentials (VECPs) are useful for investigating the mechanisms and dysfunctions of color vision. Chromatic sinusoidal gratings are generally used to elicit VECPs, but they require long psychophysical measurements to match the perceptual luminance between their stripes. An alternative method is to use pseudoisochromatic stimuli, which makes use of luminance noise to mask luminance clues and force the target perception to be dependent on chromatic contrast. In this study, we compared VECPs generated by sinusoidal gratings and pseudoisochromatic gratings. Contrary to chromatic sinusoidal gratings, pseudoisochromatic stimuli do not require the use of previous methods to find the equiluminance of the stimulus. METHODS: Normal trichromats were recruited to be tested with red-green chromatic sinusoidal gratings and pseudoisochromatic gratings presented by pattern onset-offset and pattern reversal modes in five spatial frequencies. In addition, we also tested four different chromatic contrast pairs in pattern onset-offset mode presentation in five trichromats and one colorblind subject (deuteranope). RESULTS: Pattern onset-offset VECPs elicited by sinusoidal gratings had a larger amplitude than those obtained with pseudoisochromatic stimuli, whereas pattern reversal VECPs elicited by pseudoisochromatic gratings had similar amplitudes compared to those elicited by sinusoidal gratings. We found no difference between the VECP amplitudes elicited by sinusoidal and pseudoisochromatic gratings containing different chromatic contrast. Color-blind subjects displayed absent or small responses to the stimuli. CONCLUSION: Pseudoisochromatic stimulus can be an alternative stimulus to generate VECPs dominated by the chromatic mechanism.

Assuntos

Percepção de Cores/fisiologia , Defeitos da Visão Cromática/fisiopatologia , Potenciais Evocados Visuais/fisiologia , Estimulação Luminosa , Córtex Visual/fisiologia , Adulto , Defeitos da Visão Cromática/diagnóstico , Sensibilidades de Contraste/fisiologia , Eletrorretinografia , Feminino , Humanos , Masculino , Reconhecimento Visual de Modelos , Psicofísica , Adulto Jovem

RESUMO

We describe an automated training/testing system for adult mice that allows reliable quantification of visual discrimination capacities, adaptive swimming strategies, and stereotyped choices with minimal human intervention. The experimental apparatus consists of a hexagonal swimming pool with an internal decision zone leading to three interior arms with two software-controlled platforms inside of each arm. Each experimental trial consists in projecting a "positive" conditioned discriminative stimulus (SD) in one randomly chosen arm, whereas the other two arms project non-reinforced stimuli (the delta stimuli, SΔ). By employing a classical behavioral training schedule, the mice learn to swim toward the arm that displays the SD, because it predicts the presence of two elevated platforms located symmetrically to the left and right side of the projecting monitor. Separate behavioral components for discriminative and stereotyped choice behavior can be identified through this geometric arrangement. In addition, the projection in real-time of either static or dynamic visual stimuli allows the usage of training programs contingent on current behavioral performance. We validated the system by characterizing the visual acuity and contrast sensitivities in a group of trained mice. By employing pharmacological manipulations, we found that the mice required an intact functioning of the primary visual cortex (V1) to solve the hexagonal pool. Overall, the automated training system constitutes a reliable, rapid, and inexpensive method to quantify visual capacities of mice. It can be used to characterize visual and non-visual factors of choice behavior. It can also be combined with manipulations of visual experience and pharmacological micro-infusions to investigate integrated brain function and learning processes in adult mice over consecutive days.

RESUMO

BACKGROUND: Historically, the primary sensory areas of the cerebral cortex have been exclusively associated with the processing of a single sensory modality. Yet the presence of tactile responses in the primary visual (V1) cortex has challenged this view, leading to the notion that primary sensory areas engage in cross-modal processing, and that the associated circuitry is modifiable by such activity. To explore this notion, here we assessed whether the exploration of novel objects in the dark induces the activation of plasticity markers in the V1 cortex of rats. METHODS: Adult rats were allowed to freely explore for 20 min a completely dark box with four novel objects of different shapes and textures. Animals were euthanized either 1 (n = 5) or 3 h (n = 5) after exploration. A control group (n = 5) was placed for 20 min in the same environment, but without the objects. Frontal sections of the brains were submitted to immunohistochemistry to measure protein levels of egr-1 and c-fos, and phosphorylated calcium-dependent kinase (pCaKMII) in V1 cortex. RESULTS: The amount of neurons labeled with monoclonal antibodies against c-fos, egr-1 or pCaKMII increased significantly in V1 cortex after one hour of exploration in the dark. Three hours after exploration, the number of labeled neurons decreased to basal levels. CONCLUSIONS: Our results suggest that non-visual exploration induces the activation of immediate-early genes in V1 cortex, which is suggestive of cross-modal processing in this area. Besides, the increase in the number of neurons labeled with pCaKMII may signal a condition promoting synaptic plasticity.