A simple and comprehensive method for the construction, repair and recycling of single and double tungsten microelectrodes

A low-cost protocol for reconditioning of deep-brain neural microelectrodes with material failure for electrophysiology recording

To date, a myriad of neural microelectrodes has been meticulously developed, but the focus of existing literature predominantly revolves around fabrication methodologies rather than delving into the reconditioning processes or strategies for salvaging electrodes exhibiting diminished performance due to material failure. This study aims to elucidate the underlying factors contributing to the degradation in performance of neural microelectrodes. Additionally, it introduces a comprehensive, cost-effective protocol for the reconditioning and repurposing of electrodes afflicted by material failure, tailored for a broad spectrum of electrode types. The efficacy of the proposed reconditioning protocol is substantiated through experimental validation on single-site tungsten microelectrodes. The results of neural signal recording unequivocally demonstrate the successful restoration of a substantial number of electrodes, underscoring the protocol's effectiveness.

Precise Targeting of Single Microelectrodes to Orientation Pinwheel Centers

In the mammalian visual system, early stages of visual form perception begin with orientation selective neurons in primary visual cortex (V1). In many species (including humans, monkeys, tree shrews, cats, and ferrets), these neurons are organized in pinwheel-like orientation columns. To study the functional organization within orientation pinwheels, it is important to target pinwheel subdomains precisely. We therefore developed a technique to provide a quantitative determination of the location of pinwheel centers (PCs). Previous studies relied solely on blood vessel images of the cortical surface to guide electrode penetrations to PCs in orientation maps. However, considerable spatial error remained using this method. In the present study, we improved the accuracy of targeting PCs by ensuring perpendicularity of electrodes and by utilizing the orientation tuning of local field potentials (LFP) recorded at or near the optically determined positions.

Subdomains within orientation columns of primary visual cortex

In the mammalian visual system, early stages of visual form processing begin with orientation-selective neurons in primary visual cortex (V1). In many species (including humans, monkeys, tree shrews, cats, and ferrets), these neurons are organized in a beautifully arrayed pinwheel-like orientation columns, which shift in orientation preference across V1. However, to date, the relationship of orientation architecture to the encoding of multiple elemental aspects of visual contours is still unknown. Here, using a novel, highly accurate method of targeting electrode position, we report for the first time the presence of three subdomains within single orientation domains. We suggest that these zones subserve computation of distinct aspects of visual contours and propose a novel tripartite pinwheel-centered view of an orientation hypercolumn.

Effect of Contrast on Visual Spatial Summation in Different Cell Categories in Cat Primary Visual Cortex

Multiple cell classes have been found in the primary visual cortex, but the relationship between cell types and spatial summation has seldom been studied. Parvalbumin-expressing inhibitory interneurons can be distinguished from pyramidal neurons based on their briefer action potential durations. In this study, we classified V1 cells into fast-spiking units (FSUs) and regular-spiking units (RSUs) and then examined spatial summation at high and low contrast. Our results revealed that the excitatory classical receptive field and the suppressive non-classical receptive field expanded at low contrast for both FSUs and RSUs, but the expansion was more marked for the RSUs than for the FSUs. For most V1 neurons, surround suppression varied as the contrast changed from high to low. However, FSUs exhibited no significant difference in the strength of suppression between high and low contrast, although the overall suppression decreased significantly at low contrast for the RSUs. Our results suggest that the modulation of spatial summation by stimulus contrast differs across populations of neurons in the cat primary visual cortex.

Orientation selectivity in cat primary visual cortex: local and global measurement

In this study, we investigated orientation selectivity in cat primary visual cortex (V1) and its relationship with various parameters. We found a strong correlation between circular variance (CV) and orthogonal-topreferred response ratio (O/P ratio), and a moderate correlation between tuning width and O/P ratio. Moreover, the suppression far from the peak that accounted for the lower CV in cat V1 cells also contributed to the narrowing of the tuning width of cells. We also studied the dependence of orientation selectivity on the modulation ratio for each cell, which is consistent with robust entrainment of the neuronal response to the phase of the drifting grating stimulus. In conclusion, the CV (global measure) and tuning width (local measure) are signifi cantly correlated with the modulation ratio.

The spatial summation characteristics of three categories of V1 neurons differing in non-classical receptive field modulation properties

The spatial summation of excitation and inhibition determines the final output of neurons in the cat V1. To characterize the spatial extent of the excitatory classical receptive field (CRF) and inhibitory non-classical receptive field (nCRF) areas, we examined the spatial summation properties of 169 neurons in cat V1 at high (20-90%) and low (5-15%) stimulus contrasts. Three categories were classified based on the difference in the contrast dependency of the surround suppression. We discovered that the three categories significantly differed in CRF size, peak firing rate, and the proportion of simple/complex cell number. The classification of simple and complex cells was determined at both high and low contrasts. While the majority of V1 neurons had stable modulation ratios in their responses, 10 cells (6.2%) in our sample crossed the classification boundary under different stimulus contrasts. No significant difference was found in the size of the CRF between simple and complex cells. Further comparisons in each category determined that the CRFs for complex cells were significantly larger than those for simple cells in category type I neurons, with no significant differences between simple and complex cells in category type II and type III neurons. In addition, complex cells have higher peak firing rates than simple cells.

Contrast-dependent variations in the excitatory classical receptive field and suppressive nonclassical receptive field of cat primary visual cortex

In area V1 of cat and monkey, there is a surround region beyond the classical receptive field (CRF) which alone is unresponsive but may modulate the cell's response. This field is referred to as the "nonclassical receptive field" (nCRF). It has been reported in monkey that the extent of CRF and/or nCRF of V1 neurons is not fixed but varies with stimulus contrast. We reexamined the contrast dependence of V1 neurons in cat to determine whether this differs from previous studies in macaque. By fitting the spatial summation curves obtained at different contrasts with a difference of Gaussians model, we estimated quantitatively the effect of contrast on the spatial extent of the CRF and nCRF as well as the strength of surround suppression. Our results showed that both the CRF and nCRF expanded at low contrast, but the expansion is more marked for the CRF than for the nCRF. Although the effect of contrast on surround suppression was varied, the overall suppression increased significantly at high contrast. Moreover, the contrast-dependent change in the extent of CRF is independent of the change in suppression strength. Overall, our results in cat are in agreement with those obtained in macaque money.

Excitatory and suppressive receptive field subunits in awake monkey primary visual cortex (V1)

An essential step in understanding visual processing is to characterize the neuronal receptive fields (RFs) at each stage of the visual pathway. However, RF characterization beyond simple cells in the primary visual cortex (V1) remains a major challenge. Recent application of spike-triggered covariance (STC) analysis has greatly facilitated characterization of complex cell RFs in anesthetized animals. Here we apply STC to RF characterization in awake monkey V1. We found up to nine subunits for each cell, including one or two dominant excitatory subunits as described by the standard model, along with additional excitatory and suppressive subunits with weaker contributions. Compared with the dominant subunits, the nondominant excitatory subunits prefer similar orientations and spatial frequencies but have larger spatial envelopes. They contribute to response invariance to small changes in stimulus orientation, position, and spatial frequency. In contrast, the suppressive subunits are tuned to orientations 45 degrees -90 degrees different from the excitatory subunits, which may underlie cross-orientation suppression. Together, the excitatory and suppressive subunits form a compact description of RFs in awake monkey V1, allowing prediction of the responses to arbitrary visual stimuli.

Cue-invariant detection of centre-surround discontinuity by V1 neurons in awake macaque monkey

Visual perception of an object depends on the discontinuity between the object and its background, which can be defined by a variety of visual features, such as luminance, colour and motion. While human object perception is largely cue invariant, the extent to which neural mechanisms in the primary visual cortex contribute to cue-invariant perception has not been examined extensively. Here we report that many V1 neurons in the awake monkey are sensitive to the stimulus discontinuity between their classical receptive field (CRF) and non-classical receptive field (nCRF) regardless of the visual feature that defines the discontinuity. The magnitude of this sensitivity is strongly dependent on the strength of nCRF suppression of the cell. These properties of V1 neurons may contribute significantly to cue-invariant object perception.

Spatial phase sensitivity of V1 neurons in alert monkey

The activity of V1 neurons evoked by stimuli within the classical receptive field (CRF) is known to be modulated by stimuli in the surrounding field, the extra-receptive field (ERF). By varying the relative spatial phase (RSP) between a central grating presented in the CRF and a surround grating in the ERF, we studied the contextual modulation in V1 neurons of alert monkeys (Macaca mulata). Results from two monkeys show that most of the V1 neurons with suppressive ERF are sensitive to the RSP, and the degree of sensitivity is strongly dependent on the strength of ERF suppression. This sensitivity is maximal when the RSP is generated at or near CRF/ERF boundary, but is observed over the entire ERF. Interestingly, the suppressive effect of the surround grating can be largely abolished by inserting a narrow gap between the center and surround gratings or by a phase displacement between them corresponding to <10% of the CRF diameter. These properties of V1 neurons may serve important perceptual functions.

Stimulation of non-classical receptive field enhances orientation selectivity in the cat

We have investigated how the nonclassical receptive field (nCRF) affects dynamic orientation selectivity of cells in the primary visual cortex (V1) in anaesthetized and paralysed cats using the reverse correlation method. We found that tuning to the orientation of the test stimulus depends on the size of the stimulation area. A significant sharpening of orientation tuning was induced by nCRF stimulation, with the magnitude of the effect increasing with the size of stimulation. The effect of the nCRF on the temporal dynamics of orientation tuning was also investigated by examining the tuning over a range of delays from stimulus onset. We found small but detectable changes in both the preferred orientation and the bandwidth of tuning over time when the classical receptive field (CRF) was stimulated alone. Stimulation in nCRF significantly increased the magnitude of these temporal changes. Thus, nCRF stimulation not only enhances the overall orientation selectivity, but also enriches the temporal dynamics of cortical neurones, which may increase the computational power of the visual cortex in information processing.

Clustered organization of neurons with similar extra-receptive field properties in the primary visual cortex

The primary visual cortex is organized into clusters of cells having similar classical receptive field (CRF) properties. Nonclassical, extra-receptive fields (ERFs) can either inhibit or facilitate the response elicited by stimulation within the CRF. Here, we report that in the primary visual cortex of cat, neurons with similar inhibitory or facilitatory ERF properties are also grouped into clusters. These clusters are randomly distributed in all cortical layers, with no detectable relationship with orientation and ocular dominance columns. This functional organization of neurons with respect to ERF properties may allow an efficient processing of global visual information.

A simple method for the construction of a recording-injection microelectrode with glass-insulated microwire

A rapid method for the production of a glass-insulated microwire electrode is described. A microwire was threaded into a glass capillary which was then pulled on a vertical pipette puller. A conical tip of the microwire was formed when the strongly heated glass capillary broke together with the wire in it. A tight seal of the glass-insulated microwire electrode between the glass and the metal was accomplished with silicone glue. The manufactured electrode performed consistently at different immersion depths, and yielded stable recordings of single units in the cerebral cortex and the medulla of rats. The strength and low impedance characteristics of the glass-insulated microwire electrode may make it useful for the recording of single units in deep brain structures. Furthermore, the electrode can be easily combined with another glass micropipette to form a dual recording-injection microelectrode unit.