فعالیت پتانسیل میدانی محلی در پاسخ به محرک مربعی مشکی در قشر اولیه بینایی میمون آزمایشگاهی

مقدمه: پتانسیل ‌های میدانی محلی به عنوان یک ابزار الکتروفیزیولوژیکی ارزشمند برای مطالعه عملکرد مغز عمل می ‌کنند. این سیگنال ‌ها منعکس ‌کننده فعالیت جمعی نورون ‌های همسایه هستند. از طریق استفاده از میکروالکترودهای خارج سلولی، این سیگنال‌ها از فضای باریک بافت عصبی اطراف نوک الکترود ثبت می‌شوند.روش کار: این مطالعه بر روی بررسی قشر بینایی اولیه میمون با استفاده از یک الکترود 24 کانالی تمرکز دارد. با طراحی آزمایشی شامل ارائه محرک در 36 مکان به طور تصادفی انتخاب شده، جنبه ‌های مختلف قشر بینایی، از جمله مکان میدان گیرنده، گسترش بینایی سیگنال ‌های پتانسیل میدانی محلی و زمان و دامنه قله ‌ها و دره ‌ها در لایه ‌های مختلف قشر مغز مشخص می ‌شود. برای مقایسه لایه ‌های مختلف از آزمون آماری ناپارامتریک kruskal-wallis استفاده می ‌شود.یافته ‌ها: با حرکت از لایه‌های سطحی به لایه‌های عمیق‌تر، دامنه پاسخ ابتدا کاهش و سپس افزایش می‌یابد. علاوه بر این، مکان میدان گیرنده از طریق تجزیه و تحلیل ویژگی ‌های استخراج شده از سیگنال ‌های پتانسیل میدانی محلی تعیین می ‌شود. ارزیابی گسترش بینایی کمترین مقدار گسترش را در لایه 4c در بین لایه ‌ها نشان می ‌دهد. همچنین، با بررسی زمان‌بندی قله ‌ها و دره ‌ها، بینش‌هایی در مورد ورود و خروج جریان اطلاعات در بین لایه‌ها به دست می‌آید.نتیجه ‌گیری: بررسی سیگنال‌های پتانسیل میدانی محلی مکانیسم انتشار دقیق اطلاعات در لایه‌ها را نشان می‌دهد. این نتایج به درک بهتر عملکرد قشر بینایی اولیه کمک می ‌کند و پیامدهایی برای طراحی رویکردهای رابط مغز و ماشین، پروتزهای عصبی و آنالیز سیگنال الکتروانسفالوگرافی دارد.

local field potential activity in response to a black square stimulus in the primary visual cortex

introductionthe cerebral cortex of mammals comprises six layersbetween the soft gray matter and the white brain’s white matter. the thickness of its subgroups also varies in different cortex regions. the histology and distribution of dendrites and axons also show significant variations in different cortex regions. three main thalamic pathways feed the primary visual cortex (v1) and have a unique position in receiving and distributing sensory input compared to other areas of the visual cortex. it plays a role as the first center for visual information processing in the cerebral cortex. the information that enters the visual cortex from the outside world includes complex visual scenes that need to be analyzed and broken down. neurons in the primary visual cortex transmit information about the surrounding environment and visual stimuli to higher brain regions with great precision and detail. the type of stimulus significantly affects the information present in the output signal.local field potentials (lfps) are electrical potentials generated by local electric charges distributed in an extracellular conducting medium. a better understanding of lfps can be useful in the interpretation of non-invasive human studies such as functional magnetic resonance imaging (fmri), oxygen-dependent signals, electroencephalography (eeg), and event-related potential (erp) signals. local field potentials may vary in different cortical areas and layers. recent studies suggest that lfps in high-frequency ranges may originate from a limited cortical area, contrary to previous assumptions. these signals are measured from local neuronal populations recorded by an extracellular electrode. cortical lfps are believed to bepredominantly generated by subthreshold membrane potentials in layers 2.3, 5, and 6. recording lfps is easier than spike activity and can be used in neural prostheses.in 2015, a study was conducted on the columnar organization of the visual cortex in the spatial phase (19). kozai et al. investigated methods and parameters for quantifying multi-unit recordings and local field potentials (20). martin-vazquez et al. analyzed independent components extracted from local field potential activity recorded during motor movement with rewards in multiple depths of the motor cortex to investigate their role in motor learning (21). an accurate understanding of the properties of local field potential signal responses in different layers of the cortex is crucial for future use of these signals in neural prosthetics (22). although local field potential studies have recently received attention (23-27), there has yet to be a systematic study on the response properties of local field potentials and their relationship with neighboring neuron properties (12). the main goal of neuroscience is to understand how populations of neurons are organized in different cortical areas and layers.in this study, the primary visual cortex of macaques was investigated. local field potential responses were simultaneously evaluated in all cortical layers using a 24-channel electrode. by presenting a half-degree black square stimulus and recording the response signal, the response range in different layers was investigated, and the extent of visual spread was calculated using only one electrode instead of multiple electrodes. in addition, the peak and trough time and amplitude were examined to investigate the entry and exit of information.methodsdata acquisitionthe experiment was conducted on macaque monkeys, and the data were recorded at the alessandra angelucci laboratory at the university of utah. the raw signals were continuously recorded at a sampling rate of 30 khz using a 128-channel system. it is common to filter the local field potential signals to highlight the desired activity (28). the effect of a low-pass filter on a completely inactive neuron depends on the distance between the soma and the input site and the membrane time constant. this indicates that dendritic morphology plays an essential role in frequency filtering and that pyramidal cells with their long dendrites are particularly affected by low-pass filters (29). digital filters such as gaussian filters (30), low-pass filters, butterworth filters (30-34), and zero-phase filters (30) are used in the analysis of local field potential signals. the raw recorded voltages were filtered (1-100 hz, second-order butterworth filter) and sampled up to 2 khz to obtain local field potentials.receptive field mappingthe receptive field of neurons in each column of the primary visual cortex was manually identified to determine their approximate locations. subsequently, black squares measuring 0.5° were presented within the visual field spanning 3*3°, precisely in the approximate location of the receptive field. this process identified the exact location of the receptive field for neurons within the cortical column.visual stimulusblack squares measuring 0.5° were presented within a field of view spanning 3*3°. a 24-channel linear electrode with a contact distance of 100 micrometers and a contact diameter of 20 micrometers, specifically the v-probe type manufactured by plexon, texas, was employed to record local field potentials. each stimulus within the network of these 36 blocks was presented for 500 milliseconds. the experiment was repeated between 5 to 15 times to ensure reliability and gather sufficient data.resultslocal field potential signals hold great significance in neurophysiology research and are instrumental in diagnosing neurological disorders and abnormalities within the human body. in this section, this study presents the investigation findings into the response of these signals in macaque monkeys to a visual stimulus presented in a 36-square grid.initially, the current study assessed the layers using current source density analysis. subsequently, this research analyzed the minimum response field (mrf) behavior pattern in different layers, along with the neighboring areas, utilizing the response range derived from the local field potential signal. this study focuses on analyzing the propagation of the local field potential signal. by identifying the peaks and troughs within different layers, the researchers further explore the timing and intensity of information entry and exit.given the pivotal role of local field potential signals in comprehending brain information at the cognitive level, it is crucial to study their spatial accuracy and gain a deeper understanding of how these signals are processed.figure 1. local field potential response to visual stimulus presented at the minimum receptive fieldfigure 1 (a) shows the current source density of local field potential at the minimum receptive field in the layers. the color corresponding to the sink and source is shown in the figure legend. the x-axis shows time, and the y-axis shows the depth of the cortex. figure 1 (b) indicates the local field potential response at the minimum receptive field to the presented stimulus. the upper, middle, and deep layers are indicated in the figure 1. the blue dashed line indicates the stimulus presentation time (0 milliseconds), and the pink dashed line demonstrated 50 milliseconds after the stimulus presentation.response rangecalculating the peak and trough times and values were extracted by calculating the first and second derivatives and the sign of the local potential field signal. as can be seen, this parameter evaluates the distance between the minimum and maximum values of the local potential field signal in the range under investigation (0-200 milliseconds).the response pattern is uniform in the minimum receiver field and its surrounding cells in the layers, and in the minimum receiver field, it has the maximum value in terms of range compared to its surrounding cells. as can be seen, as we move from the upper layers towards the middle layers, the response range decreases and then increases again upon reaching deeper layers. based on the results of the kruskal-wallis statistical test on the investigation of the response range across layers for the minimum receiver field and