Egocentric Distance Encoding in the Posterior Parietal Cortex

Neurons in the parietal reach region (PRR) have been implicated in the sensory-to-motor transformation required for reaching toward visually defined targets. The neurons in each cortical hemisphere might be specifically involved in planning movements of just one limb, or the PRR might code reach endpoints generically, independent of which limb will actually move. Previous work has shown that the preferred directions of PRR neurons are similar for right and left limb movements but that the amplitude of modulation may vary greatly. We now test the hypothesis that frames of reference and eye and hand gain field modulations will, like preferred directions, be independent of which hand moves. This was not the case. Many neurons show clear differences in both the frame of reference as well as in direction and strength of gain field modulations, depending on which hand is used to reach. The results suggest that the information that is conveyed from the PRR to areas closer to the motor output (the readout from the PRR) is different for each limb and that individual PRR neurons contribute either to controlling the contralateral-limb or else bimanual-limb control.

Spatial computations underlying the coordination of the hand and eye present formidable geometric challenges. One way for the nervous system to simplify these computations is to directly encode the relative position of the hand and the center of gaze. Neurons in the dorsal premotor cortex (PMd), which is critical for the guidance of arm-reaching movements, encode the relative position of the hand, gaze and goal of reaching movements. This suggests that PMd can coordinate reaching movements with eye movements. Here, we examine saccade-related signals in PMd to determine whether they also point to a role for PMd in coordinating visual-motor behavior. We first compared the activity of a population of PMd neurons with a population of parietal reach region (PRR) neurons. During center-out reaching and saccade tasks, PMd neurons responded more strongly before saccades than PRR neurons and PMd contained a larger proportion of exclusively saccade-tuned cells than PRR. During a saccade relative position coding task, PMd neurons encoded saccade targets in a relative position code that depended on the relative position of gaze, the hand, and the goal of a saccadic eye movement. This relative position code for saccades is similar to the way that PMd neurons encode reach targets. We propose that eye movement and eye position signals in PMd do not drive eye movements, but rather provide spatial information that links the control of eye and arm movements in order to support coordinated visual-motor behavior.

The parietal reach region (PRR) is known to be involved in the preparation of visually guided arm movements to single targets. We explored whether PRR encodes only the target of the next movement or, alternatively, also a subsequent goal in a double-reach sequence. Two monkeys were trained to memorize the locations of two peripheral cues and to prepare for a memory-guided delayed double-reach sequence. Upon a GO-signal they had to reach in a predefined order to both remembered target locations without breaking eye fixation. The movement goals were arranged such that either the first or the second target was inside the response field of an isolated neuron. We analyzed the neural activity of single cells in PRR during the late memory period between cue offset and the GO-signal. During this memory period, most PRR cells encoded the first as well as the second goal of the planned reaching sequence. The results indicate that the posterior parietal cortex is involved in the spatial planning of more complex action patterns and represents immediate and subsequent movement goals.

EPA-1538 - Modulation in attention related eye vergence is disrupted in children with attention deficit hyperactivity disorder

O propósito foi investigar experimentalmente o desempenho dos observadores numa original tarefa de julgamento de colinearidade em campo aberto (dimensões 20 x 30 m). Participaram do experimento 30 observadores. Os estímulos foram estacas verticais de alturas variáveis, quatro fixos e quatro móveis. A tarefa consistiu em ajustar os dois estímulos móveis (mediante controle à distância) para que ficassem colineares aos dos estímulos fixos nos extremos de cada diagonal. Foi realizada uma análise de variância (ANOVA) fatorial sobre os erros de colinearidade, revelando somente efeito significativo para o fator ‘Estímulo Móvel’ (F(3,473)=69,86 p<0,001) notando-se uma sistemática na distribuição dos erros. As pequenas variações na distância exocêntrica percebida (com erros constantes dez vezes menores que os encontrados ao avaliar as distâncias egocêntricas) e a relação dos erros cometidos com as distâncias egocêntricas indicariam que o marco de referência eliciado por esta tarefa de colinearidade, embora possa estar baseado nos indícios exocêntricos, é escalado por um fator egocêntrico.

In healthy subjects, the postural stability in orthostatic position is better when fixating at near than at far. Increase in the convergence angle contributes to this effect. Children with strabismus present a deficit in vergence. We evaluated postural control in children with respect to the vergence angle as they fixated at different depths, thereby engaging in active vergence movements. A TechnoConcept platform was used to record the postural stability of 11 subjects (mean age 11.18 ± 4.02 years) with convergent strabismus and 13 (mean age 11.31 ± 3.54 years) with divergent strabismus in 3 conditions: fixation at 40 cm, at 2 m, and active vergence movements between 20 and 50 cm. The mediolateral body sway decreased significantly with proximity for convergent strabismus (from 3.78-2.70 mm) but increased significantly for divergent strabismus (from 3.27-3.97). Relative to fixation, vergence eye movements resulted in a statistically significant increase in mediolateral body sway for convergent strabismus (3.55 vs. 2.70) and a decrease for divergent strabismus (3.11 vs. 3.97, P = 0.047). Vergence eye movements were associated with the least variance of speed (99 mm(2)/s(2) for convergent and 117 mm(2)/s(2) for divergent strabismus), so less energy was required to control body sway. The fixation depth at which postural stability is best is proximal for convergent strabismus and distal for divergent strabismus. Optimal postural stability might be mediated by preponderant eye movement signals related to the angle of strabismus. Reduction of variance of speed in the active vergence condition corroborates our hypothesis.

The current prevailing understanding of sensory processing in cortical areas is largely based on the presentation framework proposes that neural activity form presentations of external stimulus. However, with recent advances in technologies of recording neuronal activity in awake behaving animals, it has been shown that the primary visual cortex (V1) is also strongly driven by self-movement, suggesting that the presentation framework of visual cortex function is incomplete. Particularly, a subset of neurons in V1 selectively respond to transient visuomotor mismatches, and it could be explained by the predictive coding framework which postulates V1 compares the predicted and received visual input and sense the difference between the two. Experience of normal visuomotor coupling has been shown to be crucial for the development of visual-guided behavior, therefore it is likely that the prediction of visual input depends on the experience of visuomotor coupling, which shapes the functional development of V1. In the present study, we use a virtual reality system and trained dark-reared mice with either normal or random visuomotor coupling, and recorded the neural activity in layer 2/3 neurons of V1. We show that mismatch responses in excitatory neurons were strongly dependent on visuomotor experience. By recording several different types of layer 2/3 interneurons in V1 and manipulating their activity with designer receptor exclusively activated by designer drugs (DREADDs) or optogenetics tools, we propose a circuit model showing that the mismatch response could be the result of a disinhibition mediated by local somatostatin (SST) interneurons. Mismatch responses in both groups of mice with different visuomotor training conditions merged together after they were transferred to normal rearing environment. These data demonstrate that neurons in layer 2/3 mouse V1 computes a difference between an excitatory motor-related input and an inhibitory visual input, where the balance between the two inputs is finely tuned by visuomotor experience.

The role of magnesium on nerve tissue was discussed. Two main topics of "magnesium and neural activity" and "magnesium-therapy and brain neurons" were described together with introducing our research on rat cultured neurons of cortex and hippocampus.

Zebra finches memorize a tutor song as juveniles, and then faithfully reproduce this song for the remainder of their lives. This thesis investigates how the intricate and concerted activity of ensembles of neurons in the zebra finch brain gives rise to this complex behavior. The first section of the thesis demonstrates how neurons in RA, a pre-motor song control nucleus, coordinate their activity to generate the instantaneous spectral and temporal structure seen in the song. Similar sounds are produced by entirely different ensembles of RA neurons. Additionally, rapidly changing patterns of RA neural activity are capable of generating constant acoustic outputs. This is a new form of neural coding, previously unobserved in any other system. This unusual neural representation provides a concise account of an unexplained aspect of song learning. The second part of the thesis develops a new, noninvasive method of altering the auditory feedback heard by singing zebra finches. This type of feedback perturbation causes the normally stable songs of adult birds to deteriorate, indicating that auditory feedback is essential to song control throughout life. Restoration of the normal auditory feedback heard by these birds enables the gradual recovery of their original songs, demonstrating that a memory of the original song persists in the song control system despite the destabilization of the behavior. The song is thus maintained by an active feedback control process. The final project investigates the role of nucleus LMAN in real-time song control via auditory feedback. Neurons in nucleus LMAN were previously believed to compare auditory feedback to a memorized song template. The result of this comparison was thought to be used as an error-correction signal to update the motor control program. By recording from individual LMAN neurons while simultaneously manipulating the auditory feedback heard by the singing bird, it is shown that during singing, rather than auditory feedback, LMAN processes an efference copy of the motor commands used to generate the bird's song. This suggests a different model of the system, in which the efference copy is the basis of the real-time error-correction signal. Taken together, these three projects significantly expand our knowledge of the neural mechanisms responsible for the generation of birdsong.

In line with a possible role of vergence in orienting visual attention, we sought to study this eye movement in young children to provide insights on face perception. For this purpose, we measured the modulation in the angle of eye vergence in a sample of 39 children aged 6-36 months and compared it when presenting static human face images versus their scrambled version. We observed enhanced vergence responses to faces compared with scrambled images. Our data suggest a role of eye vergence in face processing.

Is a dialogue between neurophysiological research and psychiatric research possible? It is possible that such an exchange would allow us to understand what makes our brain “human”? We are able to identify two fundamental moments in the functional development of the cortex: the 24th week and the moment of birth. At the 24th week, with the formation of the subplate zone and the retina, the capacity to react appears, allowing the foetus, in case of birth, to react to the luminous stimulation. There is at the moment of birth a real and proper break between the foetal state and the neonatal state. From the physiological point of view this difference is characterized by the activation of the immediate early genes by sensorial stimulation, the activation of the cerebral cortex through the locus coeruleus by luminous stimulation, by the switch of the neurotransmitters through the formation of the inhibitory and excitatory systems. The two physiological concepts of inhibition and excitation are surpassed in the creation of a different temporal organization among the neuronal populations. At the moment of birth there is a rapid passage from foetal endogenous neural activity that expresses itself through SATs tracing, to one that is stimulus-induced and expresses itself with the onset of continuous oscillatory activity. This neurophysiological data confirms what has been theorized, following a deductive method, by Massimo Fagioli, that when the light stimulates the retina, at the moment of birth, the cerebral cortex is activated.

An EEG signal is a measurement of currents that flow during synaptic excitations of the dendrites of many pyramidal neurons in the cerebral cortex.EEG is used to denote electrical neural activity of the brain. Electroencephalography (EEG) is the recording of electric potentials produced by the local collective partial synchrony of electrical field activity in cortical neuropile, today most commonly measured by an array of electrodes attached to the scalp using water-based gel.

With the rapid advancements in user demands and technological innovation, ultra‐thin and lightweight laptops have emerged as a key trend in the evolving market landscape. However, balancing extreme slimness with the maintenance of structural integrity and optical performance remains a significant design challenge. Despite ongoing progress in thin and light technologies, achieving an optimal design that harmonizes these competing factors remains a pressing concern. This paper introduces an innovative module design approach aimed at striking the optimal balance between minimizing thickness and enhancing performance, providing novel insights for future notebook computer designs.In this study, several critical design optimizations were implemented. First, the thickness of the module was substantially reduced by thinning the PCBA, glass substrate, and polarizer. Second, the back cover design was eliminated, and the reflector was integrated into the center frame, thereby streamlining the overall module structure. Finally, the use of ultra‐thin composite films, light guide plates, and miniaturized LEDs further reduced the module's thickness.Throughout the optimization process, several challenges were encountered, including compromised module strength, light leakage caused by deformation, and the firefly effect. To address these issues, effective solutions were proposed. Firstly, a metal middle frame replaced the traditional PC frame, and an all‐aluminum A‐cover was incorporated to significantly enhance structural strength. Secondly, an all‐aluminum B‐cover was utilized to compress the module edges, mitigating the risk of light leakage due to deformation. Lastly, the light guide plate was optimized, and black ink was applied to the edges of the optical film to effectively suppress the firefly effect.Ultimately, this study successfully developed an ultra‐thin NB module with a thickness of 0.99 mm and a weight of 99 grams. This module not only satisfies the growing market demand for ultra‐thin laptops but also maintains exceptional structural integrity and optical performance, providing valuable insights for the industry and laying the groundwork for future advancements in Slim technology.

How do we find a target object in a cluttered visual scene? Targets carrying unique salient features can be found in parallel without directing attention, whereas targets defined by feature conjunctions or non-salient features need to be scrutinized in a serial attentional process in order to be identified. In this article, we review a series of experiments in which we used fMRI to probe the neural basis of this active search process in the human brain. In all experiments, we compared the fMRI signal between a difficult and an easy visual search (each performed without eye movements) in order to isolate neural activity reflecting the search process from other components such as stimulus responses and movement-related activity. The difficult search was either a conjunction search or a hard feature search and compared with an easy feature search, matched in visual stimulation and motor requirements. During both, the conjunction search and the hard feature search the frontal eye fields (FEF) and three parietal regions located in the intraparietal sulcus (IPS) were differentially activated: the anterior and posterior part of the intraparietal sulcus (AIPS, PIPS) as well as the junction of the intraparietal with the transverse occipital sulcus (IPTO). Only in PIPS, the modulation strength was most indistinguishable between conjunction and hard feature search. In a further experiment we showed that AIPS and IPTO are involved in visual conjunction search even in the absence of distractors; by contrast, the involvement of PIPS seems to depend on the presence of distractors. Taken together, these findings from these experiments demonstrate that all four key nodes of the human ’frontoparietal attention network’ are generally engaged in the covert selection process of visual search. But they also suggest that these areas play differential roles, perhaps reflecting different sub-processes in active search. We conclude by discussing a number of such sub-processes, such as the direction of spatial attention, visual feature binding, and the active suppression of distractors.

Selective attention can be a useful tactic for speech-in-noise (SiN) interpretation as it strengthens cortical responses to attended sensory inputs while suppressing others. This cortical process is referred to as attentional modulation. Our earlier study showed that a neurofeedback training paradigm was effective for improving the attentional modulation of cortical auditory evoked responses. However, it was unclear how such neurofeedback training improved attentional modulation. This paper attempts to unveil what neural mechanisms underlie strengthened auditory selective attention during the neurofeedback training paradigm. Our EEG time–frequency analysis found that, when spatial auditory attention was focused, a fronto-parietal brain network was activated. Additionally, the neurofeedback training increased beta oscillation, which may imply top-down processing was used to anticipate the sound to be attended selectively with prior information. When the subjects were attending to the sound from the right, they exhibited more alpha oscillation in the right parietal cortex during the final session compared to the first, indicating improved spatial inhibitory processing to suppress sounds from the left. After the four-week training period, the temporal cortex exhibited improved attentional modulation of beta oscillation. This suggests strengthened neural activity to predict the target. Moreover, there was an improvement in the strength of attentional modulation on cortical evoked responses to sounds. The Placebo Group, who experienced similar attention training with the exception that feedback was based simply on behavioral accuracy, did not experience these training effects. These findings demonstrate how neurofeedback training effectively improves the neural mechanisms underlying auditory selective attention.