Multi-electrode recording from the developing visual pathway of awake behaving ferrets

We have developed an effective technique for obtaining multi-electrode extracellular recordings from developing lateral geniculate nucleus (LGN) and visual cortex in awake behaving ferrets. Using this approach, we have been studying changes in the spatio-temporal patterns of spontaneous activity within the visual pathway during pre eye-opening development. In this paper, we describe the fabrication and implantation of 8- and 16-channel drivable multi-electrode arrays, which enable us to obtain high-quality multi-unit recordings from nearly 100% of our recording sites.     

A novel electrode-pipette design for simultaneous recording of extracellular spikes and iontophoretic drug application in awake behaving monkeys

We developed a novel design of an electrode-pipette combination (EPC) which allows access to brain structures in awake behaving primates without the need for guide tubes or to mechanically open the dura prior to electrode insertion. The EPC consists of an etched tungsten in glass electrode flanked by two pipettes which allow for local and highly controlled iontophoretic administration of neuroactive substances. These EPCs have excellent single cell isolation properties and are sturdy enough to penetrate the primate dura for up to 8 weeks following either a craniotomy or a dura scrape (i.e. even after substantial built up of fibrous scar tissue). We show that the EPCs can be used to selectively manipulate the cholinergic system in primate V1 during passive fixation and while animals perform an attentionally demanding task.     

Methods of single unit recording from medullary neural substrates in awake, behaving guinea pigs

An electrophysiological procedure that permits extracellular single neuronal recording in the medulla of unanesthetized, freely behaving animals is described. System components consist of 1) a flexible, single-strand microwire as recording electrode; 2) a miniature, skull-mounted miniature microdrive used for isolation of single unit activity; and 3) a head-mounted voltage follower that conditions and stabilizes the neuronal signals prior to amplification and transmission for further processing. A unique advantage of this procedure is the latitude and provision for microwire replacement in the event that multiple penetrations are desired or the tip of the microwire recording electrode is insulated as a result of gliomatosis. With minor modification, this technique can be used for single unit recording virtually anywhere along the supra-segmental neuraxis. Technical aspects of this procedure, together with details of design and fabrication of implantable devices, chronic instrumentation procedure, and potentials for other chronic applications, are discussed.     

Bi-directional interactions between visual areas in the awake behaving cat

The study of the cooperativity among cortical areas is essential to our understanding of brain functioning. Here we investigated the relative contributions of top-down and bottom-up directed interactions between area 17 and area 7 of the cat visual system. Bipolar local field potentials were recorded while the animals performed a go/no-go task or were in a quiet resting state. The data were analyzed by applying measures of interaction based on the Wiener-Granger causality concept. We found that during the visual task top-down directed interactions were of a similar magnitude as the bottom-up component. Second, interareal couplings tended to increase in conditions requiring a discriminative effort. Third, during behaviors not dominated by visual processing non-directed interactions increased.     

Stimulation of the nucleus accumbens as behavioral reward in awake behaving monkeys

It has been known that monkeys will repeatedly press a bar for electrical stimulation in several different brain structures. We explored the possibility of using electrical stimulation in one such structure, the nucleus accumbens, as a substitute for liquid reward in animals performing a complex task, namely visual search. The animals had full access to water in the cage at all times on days when stimulation was used to motivate them. Electrical stimulation was delivered bilaterally at mirror locations in and around the accumbens, and the animals' motivation to work for electrical stimulation was quantified by the number of trials they performed correctly per unit of time. Acute mapping revealed that stimulation over a large area successfully supported behavioral performance during the task. Performance improved with increasing currents until it reached an asymptotic, theoretically maximal level. Moreover, stimulation with chronically implanted electrodes showed that an animal's motivation to work for electrical stimulation was at least equivalent to, and often better than, when it worked for liquid reward while on water control. These results suggest that electrical stimulation in the accumbens is a viable method of reward in complex tasks. Because this method of reward does not necessitate control over water or food intake, it may offer an alternative to the traditional liquid or food rewards in monkeys, depending on the goals and requirements of the particular research project.     

Multiple-joint neurons in somatosensory cortex of awake monkeys

(1) The somatosensory cortex of alert monkeys, 55 neurons were found which receive convergent information from two or more adjacent joints. Most of these multiple-joint neurons were excited by postures of the hand, particularly those involved in grasping.

(2) Three basic types of joint interactions were observed. The simplest neurons (occlusion neurons) responded to postures of several different joints, but combination of the preferred postures produced no further increase in firing. The more complex cells showed summated responses to combined postures of adjacent joints, or subliminal facilitation between joints. The responses of both summation neurons and subliminal facilitation neurons were graded with joint angle, and there was an optimum or preferred position for both joints which gave the strongest response.

(3) Multiple-joint neurons may provide a neuronal substrate for extracting postural information from several different populations of kinesthetic neurons. They therefore act as feature-detecting neurons, abstracting information about specific body postures.

Steady-state visual evoked responses in anesthetized monkeys

Steady-state stimuli are repeated continuously at a frequency that evokes averaged EEG waveforms with components at a frequency which is the same or some multiple of the stimulus rate. A variety of stimulus parameters are readily manipulated and controlled. We wished to assess the suitability of this approach for animal experimentation, and chose to evaluate steady-state visual evoked potential (VEP) responses to counterphased checkerboard stimuli in anesthetized adult male Rhesus monkeys. Large VEPs were reliably produced over the range of 3–6 Hz reversal rate; at 10 Hz, the VEP spectral power was clearly diminished in all monkeys. At each given reversal rate, monkeys differed substantially in variability and amount (up to 3-fold) of spectral power. These large inter-subject differences paralleled what we have seen in similar studies of unanesthetized humans. All monkeys developed large VEPs at the midline, but the topographic distribution of maximum VEP was not uniform; in 3 monkeys the power was much greater over one hemisphere than the other. Fatigue or habituation was not evident; in each monkey, there were usually no significant differences in VEP power over the 3 consecutive 30 sec segments of a given stimulation. We conclude that the anesthetized monkey can be a suitable model for study of steady-state phenomena, as long as the proper stimulus parameters are employed and as long as the level of variance is taken into account.     

Single cell activity in ventral prefrontal cortex of behaving monkeys

Single unit activity was recorded extracellularly from ventral prefrontal cortex (VPC) of monkeys during performance of two short-term memory tasks: spatial delayed response and delayed matching to sample. The tasks required perception, retention and recognition of visual cues differing in either color or spatial location. Two separate areas of VPC were explored: a lateral area in the lower prefrontal convexity and a medial area around the medial orbital sulcus.Two categories of unit activity were distinguished on the basis of frequency changes to the cue. One was characterized by non-specific discharge independent upon which cue was presented, the other by discriminative discharge related not only to visual qualities of the cue but to the animal's subsequent use of it. Nearly one-half of all units showed altered firing during the retention (delay) period as compared with intertrial control firing. Eighteen per cent displayed delay activity related to the quality of the preceding cue. The lateral and medial segments of VPC were not distinguished by differences of unit activity in cue or delay periods.Post-trial activity was related to presence or absence of reward. Type I cells showed firing changes following choice reinforcement as well as gratuitous reward; some showed changes in opposite direction following unreinforced choices. They may encode the availability of reward. Type II cells showed changes of activity after unreinforced trials and, in some cases, opposite changes after unexpected reward; they were not affected by the reward of normal correct-choice trials. These cells appear to react to deviations from expectancy of reward. Type III cells exhibited comparable firing changes following reinforced and unreinforced choices. They may encode termination of a trial sequence. Type I was more common in lateral than medial VPC, whereas the opposite was true for type II; type III did not clearly predominate in either area.Ablation studies have shown that the two areas of VPC differe in behavioral functions. This study of their cellular properties revealed topographic differences only during the post-trial period. It is therefore possible that the combination of cue and delay activity (related to exteroceptive input) with post-trial activity (related to interoceptive input) constitutes the neuronal basis for the two areas' differences in behavioral function.     

Methods for chronic neural recording in the telencephalon of freely behaving fish

We have adapted for use in fish several of the procedures employed for recording single neuron activity in freely behaving rodents. Developing a method for single unit chronic recording in freely behaving fish was motivated by a need for a comparison across taxa of telencephalic neural activity evoked during spatial navigation by animals of their environments. However, the procedures outlined here can be modified easily for underwater recording from most aquatic species and from other brain areas. Under anesthesia, bundles of stereotrodes or tetrodes were implanted into the dorsolateral region of the goldfish or cichlid telencephalon. An infrared light emitting diode (LED) was also fixed to the fish's head at the time of surgery. After recovery from anesthesia, fish were allowed to swim freely within a large aquarium. Single unit activity was analyzed and correlated with stimulus conditions, behavior, and the location and movement of the LED recorded by a camera tracking system. The value of this technique is demonstrated by providing the first evidence in fish for navigation-related neural firing, including "place cells" that display location-specific discharge.     

Methods for functional magnetic resonance imaging in normal and lesioned behaving monkeys

Methods for performing functional magnetic resonance imaging (fMRI) studies in behaving and lesioned monkeys using a human MR scanner are reported. Materials for head implant surgery were selected based on tests for magnetic susceptibility. A primate chair with a rigid head fixation system and a mock scanner environment for training were developed. To perform controlled visual studies, monkeys were trained to maintain fixation for several minutes using a novel training technique that utilized continuous juice rewards. A surface coil was used to acquire anatomical and functional images in four monkeys, one with a partial lesion of striate cortex. High-resolution anatomical images were used after non-uniform intensity correction to create cortical surface reconstructions of both lesioned and normal hemispheres. Our methods were confirmed in two visual experiments, in which functional activations were obtained during both free viewing and fixation conditions. In one experiment, face-selective activity was found in the fundus and banks of the superior temporal sulcus and the middle temporal gyrus in monkeys viewing pictures of faces and objects while maintaining fixation. In a second experiment, regions in occipital, parietal, and frontal cortex were activated in lesioned and normal animals viewing a cartoon movie. Importantly, in the animal with the striate lesion, fMRI signals were obtained in the immediate vicinity of the lesion. Our results extend those previously reported by providing a detailed account of the technique and by demonstrating the feasibility of fMRI in monkeys with lesions.     

Double-barreled electrode for simultaneous iontophoresis and single unit recording during movement in awake monkeys

A double-barreled electrode for simultaneous glutamate iontophoresis and chronic single unit recording from cortical neurons in awake monkeys during voluntary movement is described. Electrode assembly consists of pulling a heated, partitioned capillary tube over a sharpened tungsten rod. Glutamate iontophoresis increased the firing rates of wrist movement related cells an average of 34 Hz during the agonist phase of movement and 27 Hz during the antagonist phase of movement. However, in no case did glutamate iontophoresis alter the detailed structure of the cell's response pattern during wrist movement. This electrode is well suited to chronic recording applications that involve methods such as cross-correlation requiring overlapping activity of neurons and/or muscles. Other applications might involve activation of totally 'silent' neurons to avoid possible sampling bias or to detect effects in post-stimulus time histograms that would otherwise be subliminal.     

Properties of kinesthetic neurons in somatosensory cortex of awake monkeys

(1) To study neural mechanisms used to encode kinesthetic information in somatosensory cortex of awake monkeys, we recorded from 227 single neurons responsive to joint movement or specific postures of the forelimb or hand (kinesthetic neurons). Unit responses were characterized quantitatively with respect to: (a) firing patterns; (b) responses to ramp changes in joint position and joint velocity; and (c) responses to sinusoidal joint movements.

(2) Kinesthetic neurons were divided into 3 groups. Rapidly-adapting neurons (44%) responded only to joint movement, giving a burst of impulses proportional to velocity. They showed no tonic responses to limb posture. Two populations of tonically active neurons were observed: slowly-adapting neurons (43%) and postural neurons (13%). Both types increased their firing rates with increasing degrees of flexion or extension, showing maximum excitation at the extremes of joint position in the preferred direction. They were distinguished by their sensitivity to the velocity of movement, the size of the angle over which they respond, and the phase relation of their responses to sinusoidal joint movement.

(3) The firing rates of kinesthetic neurons in S-I cortex are functions of both joint angle and joint velocity. The importance of each component varies in the 3 classes: velocity of movement is the most important determinant of firing rates of rapidly-adapting and slowly-adapting kinesthetic neurons, and joint angle predominates the responses of postural neurons.

Response dynamics of entorhinal cortex in awake, anesthetized, and bulbotomized rats

The steady-state rate of glucose oxidation through the mitochondrial TCA cycle (V(TCA)) was measured in acid extracts of 10- and 30-day-old cerebral cortex of rats receiving [1-13C]glucose intravenously and in neocortical slices superfused in vitro with the same isotope. TCA cycle flux was determined for each age group based on metabolic modeling analysis of the isotopic turnover of cortical glutamate and lactate. The sensitivity of the calculated rates to assumed parameters in the model were also assessed. Between 10 and 30 postnatal days, V(TCA) increased by 4.3-fold (from 0.46 to 2.0 micromol g(-1) min(-1)) in the cortex in vivo, whereas only a 2-fold (from 0.17 to 0.34 micromol g(-1) min(-1)) increase was observed in neocortical slices. The much greater increase in glucose oxidative metabolism of the cortex measured in vivo over that measured in vitro as the cortex matures suggests that function-related energy demands increase during development, a process that is deficient in the slice as a result of deafferentiation and other mechanisms.     

Mapping the body representation in the SI cortex of anesthetized and awake rats

We have used single unit recording techniques to map the representation of cutaneous and joint somatosensory modalities in the primary somatosensory (SI) cortex of both anesthetized and awake rats. The cytoarchitectonic zones within the rat SI were divided into the following main categories: (1) granular zones (GZs)--areas exhibiting koniocortical cytoarchitecture (i.e., containing dense aggregates of layer IV granule cells), (2) perigranular zones (PGZs)--narrow strips of less granular cortex surrounding the GZs, and (3) dysgranular zones (DZs)--large areas of dysgranular cortex enclosed within the SI. The narrow strip between the SI and the rostrally adjacent frontal agranular cortex was termed the "transitional zone" (TZ). Initial computer-based studies of the properties of cutaneous receptive fields (RFs) in SI showed that, although there were differences in response threshold, adaptability, frequency response, and overall RF size and shape of adjacent neurons, the size and location of the "centers" of the RFs were quite constant and were similar to those seen in multiple unit recordings. The same was true of RFs of single neurons recorded through different anesthetic states. The body representation in SI was first mapped by determining single unit and unit cluster RFs within a total of 2,170 microelectrode penetrations in barbiturate-anesthetized rats. Cutaneous RFs in the GZs were quite discrete. Thus, a single, finely detailed, continuous map of the cutaneous periphery was definable within the GZs themselves. Only the forepaw had a double representation. RFs in the PGZs were larger and more diffuse, but since they covered roughly the same skin areas as the RFs in the most closely adjacent GZs, they fit into the same body map. Neurons in the DZs were unresponsive to any sensory stimuli in the anesthetized animal. In chronically implanted, freely moving, awake animals cutaneous RFs were larger and more volatile than in the anesthetized, but the accuracy of the map was clearly preserved by the fact that the locations of the RF centers (which often must be defined quantitatively) were unchanged. The PGZs and DZs in the awake animals exhibited a multimodal convergence of cutaneous and joint movement RFs within single vertical penetrations, or even on single neurons. Directionally specific and bilateral cutaneous RFs were also observed in the DZs. It was concluded the DZs are more associational or integrative areas within the SI, but they could not be shown to comprise a distinct and separate body representation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Response dynamics of entorhinal cortex in awake, anesthetized, and bulbotomized rats

The generation of oscillatory activity may be crucial to brain function. The coordination of individual neurons into rhythmic and coherently active populations is thought to result from interactions between excitatory and inhibitory cells mediated by local feedback connections. By using extracellular recording wires and silicon microprobes to measure electrically evoked damped oscillatory responses at the level of neural populations in the entorhinal cortex, and by using current-source density analysis to determine the spatial pattern of evoked responses, we show that the propagation of activity through the cortical circuit and consequent oscillations in the local field potential are dependent upon background neural activity. Pharmacological manipulations as well as surgical disconnection of the olfactory bulb serve to quell the background excitatory input incident to entorhinal cortex, resulting in evoked responses without characteristic oscillations and showing no signs of polysynaptic feedback. Electrical stimulation at 200 Hz applied to the lateral olfactory tract provides a substitute for the normal background activity emanating from the bulb and enables the generation of oscillatory responses once again. We conclude that a non-zero background level of activity is necessary and sufficient to sustain normal oscillatory responses and polysynaptic transmission through the entorhinal cortex.     

Methods for recording the jaw-opening reflex to tooth-pulp stimulation in awake cats

Techniques are described for use in awake, unrestrained cats which enable recordings to be made from the digastric muscle, electrical stimuli to be applied to the teeth, and intravenous injections to be made via an indwelling cannula. A headpiece was fixed to the skull of the animal and leads were passed subcutaneously from it to electrodes in the muscle and the teeth. A silicone rubber cannula was inserted into the external jugular vein and connected to an injection port in the headpiece. The headpiece incorporated a miniature 9-way connector which was connected to the electrode leads.     

Interocular temporal delay sensitivity in the visual cortex of the awake monkey.

Due to the separation of the eyes, temporal retinal disparities are created during binocular stimulation and they have been proposed to be the basis of several stereo-visual effects. This paper studies the sensitivity of cortical neurons from area V1 to interocular temporal delay in the awake monkey (Macaca mulatta). Forty-four cells were included in this study. Temporal delay sensitivity was observed in 59% of them. About half of these temporal-delay-sensitive cells were also sensitive to the stimulation sequence of the eyes. The cells that preferred one eye to be stimulated first were termed asymmetrical (46%); those which were not sensitive to the eye sequence of stimulation were termed symmetrical (54%). No clear differences were observed in the distribution of delay-sensitive cells according to their eye dominance. Fifty-six percent of balanced cells and 65% of unbalanced cells were sensitive to interocular delay. These data underline the importance of temporal cues for depth perception.     

A method for recording single-cell activity in the frontal-pole cortex of macaque monkeys

Neurophysiological research has explored most of the prefrontal cortex of macaque monkeys, but the relatively inaccessible frontal-pole cortex remains unexamined. Here we describe a method for gaining access to the frontal-pole cortex with moveable microelectrodes. The key innovation is a direct approach through the frontal air sinus. In addition, the small size of the frontal-pole cortex in macaques led to the design of a smaller recording chamber than typically used in behavioral neurophysiology. The method has proven successful in two subjects, with no adverse health consequences.     

Activity of inferior temporal neurons in behaving monkeys.

The activity of neurons in inferior temporal cortex of behaving monkeys was studied under the following conditions: (1) in untrained animals as they spontaneously fixated visual stimuli, (2) in an animal with immobilization of one eye after section of the oculomotor nerves, (3) during performance of a visual discrimination task and (4) during performance of a visual recent memory task. When stimulated through the immobilized eye, the properties of inferior temporal were similar to those seen under anesthesia and total immobilization. Under the other conditions, the response properties of inferior temporal neurons appeared to be modulated by attentional and situational variables.