Attentional modulation of firing rate varies with burstiness across putative pyramidal neurons in macaque visual area V4.

One of the most well established forms of attentional modulation is an increase in firing rate when attention is directed into the receptive field of a neuron. The degree of rate modulation, however, can vary considerably across individual neurons, especially among broad spiking neurons (putative pyramids). We asked whether this heterogeneity might be correlated with a neuronal response property that is used in intracellular recording studies to distinguish among distinct neuronal classes: the burstiness of the neuronal spike train. We first characterized the burst spiking behavior of visual area V4 neurons and found that this varies considerably across the population, but we did not find evidence for distinct classes of burst behavior. Burstiness did, however, vary more widely across the class of neurons that shows the greatest heterogeneity in attentional modulation, and within that class, burstiness helped account for differences in attentional modulation. Among these broad spiking neurons, rate modulation was primarily restricted to bursty neurons, which as a group showed a highly significant increase in firing rate with attention. Furthermore, every bursty broad spiking neuron whose firing rate was significantly modulated by attention exhibited an increase in firing rate. In contrast, non-bursty broad spiking neurons exhibited no net attentional modulation, and, although some individual neurons did show significant rate modulation, these were divided among neurons showing increases and decreases. These findings show that macaque area V4 shows a range of bursting behavior and that the heterogeneity of attentional modulation can be explained, in part, by variation in burstiness.

Dynamic Hippocampal Circuits Support Learning- and Memory-Guided Behaviors.

The ability to learn spatial relationships and to modify stored representations when the world changes is essential for survival. In recent years, our understanding of the neural activity that underlie these learning and memory processes has improved considerably, in large part to an increase in the number of studies that use electrophysiological recordings as animals learn about their environments. In this review, we summarize some key findings from our laboratory, with a focus on recent discoveries that indicate that the rat hippocampus supports learning and decision-making behaviors via dynamic and smooth transitions in neural representation, internal processing state, and coupling with related brain structures.

Towards a large-scale recording system: demonstration of polymer-based penetrating array for chronic neural recording.

The brain is a massively interconnected network of specialized circuits. Even primary sensory areas, once thought to support relatively simple, feed-forward processing, are now known to be parts of complex feedback circuits. All brain functions depend on millisecond timescale interactions across these brain networks. Current approaches cannot measure or manipulate such large-scale interactions. Here we demonstrate that polymer-based, penetrating, micro-electrode arrays can provide high quality neural recordings from awake, behaving animals over periods of months. Our results indicate that polymer electrodes are a viable substrate for the development of systems that can record from thousands of channels across months to years. This is our first step towards developing a 1000+ electrode system capable of providing high-quality, long-term neural recordings.

Attention-dependent reductions in burstiness and action-potential height in macaque area V4.

Attention improves the encoding of visual stimuli. One mechanism that is implicated in facilitating sensory encoding is the firing of action potentials in bursts. We tested the hypothesis that when spatial attention is directed to a stimulus, this causes an increase in burst firing to the attended stimulus. To the contrary, we found an attention-dependent reduction in 'burstiness' among putative pyramidal neurons in macaque area V4. We accounted for this using a conductance-based Hodgkin-Huxley style model in which attentional modulation stems from scaling excitation and inhibition. The model exhibited attention-dependent increases in firing rate and made the surprising and correct prediction that when attention is directed into a neuron's receptive field, this reduces action-potential height. The model thus provided a unified explanation for three distinct forms of attentional modulation, two of them previously undescribed, and implicates scaling of the responses of excitatory and inhibitory input populations in mediating attention.