Single-cell activity in cat motor cortex. II. Functional characteristics of the cell related to conditioning changes

A nonparametric approach for detection of bursts in spike trains

In spike-train data, bursts are considered as a unit of neural information and are of potential interest in studies of responses to any sensory stimulus. Consequently, burst detection appears to be a critical problem for which the Poisson-surprise (PS) method has been widely used for 20 years. However, this method has faced some recurrent criticism about the underlying assumptions regarding the interspike interval (ISI) distributions. In this paper, we avoid such assumptions by using a nonparametric approach for burst detection based on the ranks of ISI in the entire spike train. Similar to the PS statistic, a "Rank surprise" (RS) statistic is extracted. A new algorithm performing an exhaustive search of bursts in the spike trains is also presented. Compared to the performances of the PS method on realizations of gamma renewal processes and spike trains recorded in cat auditory cortex, we show that the RS method is very robust for any type of ISI distribution and is based on an elementary formalization of the definition of a burst. It presents an alternative to the PS method for non-Poisson spike trains and is simple to implement.

Suppression of cortical representation through backward conditioning

Temporal stimulus reinforcement sequences have been shown to determine the directions of synaptic plasticity and behavioral learning. Here, we examined whether they also control the direction of cortical reorganization. Pairing ventral tegmental area stimulation with a sound in a backward conditioning paradigm specifically reduced representations of the paired sound in the primary auditory cortex (AI). This temporal sequence-dependent bidirectional cortical plasticity modulated by dopamine release hypothetically serves to prevent the over-representation of frequently occurring stimuli resulting from their random pairing with unrelated rewards.

Conditioning of single units in visual association cortex: cell-specific behavior within a small population

These experiments examine the interrelationships between the activity of adjacent neurons during learning. Does learning depend on coherent behavior in a population of neurons or does it depend on particular neurons engaging in a particular activity at specific times? A second purpose was to examine specificity in response modification as a function of reinforcement contingency. Cells from visual association cortex of locally anesthetized, paralyzed cats and rabbits were studied with extracellular microelectrodes capable of recording single and multiunit activity, as well as local field potentials. Multiunit records were fractionated by amplitude "windows" discrimination. Pavlovian discriminative conditioning procedures were used to evaluate selective plasticity. Cells that were activated by at least two different visual stimuli were selected. Only one of the effective stimuli was paired with foot-shock (reinforcement). Of the 180 cells or cell clusters studied, 27% exhibited conditioned modification to the reinforced stimulus (CS+) and 19% changed their response pattern to the unreinforced stimulus (CS-). None of the well isolated cells showed conditioning to both CS+ and CS-. Thus, cellular plasticity was specific to reinforcement contingency. These results provide a first demonstration of reinforcement-dependent functional distinctiveness at the neuronal level. Some cells showed no alteration of response pattern despite a most prolonged conditioning procedure. Neighboring cells, responsive to the same stimuli, revealed increases or decreases in firing rate, selective changes in the latency or amplitude of single response peaks, or the appearance of one or more new peaks as a function of conditioning. Rarely did adjacent cells show the same type of alteration when alteration occurred; there was no general tendency toward coherent firing patterns as conditioning proceeded.

Influence of thalamic cooling on sensory responses in association cortex

Evoked responses to light flash, click, and paw stimuli were recorded in the four cortical association areas in the acutely prepared cat. Average evoked responses (AEP) for 100 trials were formed before, during, and after localized cooling in the midline thalamus. Cooling of the midline thalamus reduced the magnitude of responses to click and paw stimuli, and increased or did not change the responses to light flash. There was very little similarity in trial-to-trial fluctuations of EP magnitude across cortical areas, and cooling did not reduce the similarity that existed. Waveform similarity was reduced by cooling for responses across the cortex to a single stimulus modality, whereas similarity of responses in a single cortical area to all three stimuli was not changed. The temporal components of the AEP influenced by thalamic cooling were different for different stimuli and cortical locations. It was concluded that the midline thalamo-cortical projection through the centromedian area to association cortices is particularly well-differentiated for multisensory responses in a single cortical region, and that the system should not be thought of as nonspecific but as convergent or multisensory.

Mesencephalic multiple-unit activity during acquisition of conditioned pupillary dilation

Multiple-unit recordings were obtained from the interstitial nucleus of Cajal, nucleus of Darkschewitsch and the superior colliculus of the cat during acquisition of classically conditioned pupillary dilation. Multiple-unit responses in all regions were enhanced by conditioning procedures. However, only the acquisition functions for the accessory oculomotor nuclei, i.e., interstitial nucleus of Cajal and nucleus of Darkschewitsch, were significantly correlated with the acquisition of conditioned pupillary dilation. These results were discussed in relation to the mechanism of autonomic control of conditioned pupillary dilation. It was concluded that inhibition of parasympathetic pupillomotor efferents via the accessory oculomotor nuclei may play a role in the acquisition of conditioned pupillary dilation.

Classical nictitating membrane conditioning in the awake, normal, restrained cat

Present knowledge of its central nervous system makes the cat a desirable subject for studies of brain-behavior relationships. Response frequencies and latency characteristics in conditioning and control groups indicate that the response of the nictitating membrane can be classically conditioned in a new restraint system in which detailed brain and behavior measures can be easily obtained.