Summation

About: Summation is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 45593 citations. The topic is also known as: summation & sum of a sequence.

Selective Functional Interactions between Excitatory and Inhibitory Cortical Neurons and Differential Contribution to Persistent Activity of the Slow Oscillation

Abstract: The neocortex depends upon a relative balance of recurrent excitation and inhibition for its operation. During spontaneous Up states, cortical pyramidal cells receive proportional barrages of excitatory and inhibitory synaptic potentials. Many of these synaptic potentials arise from the activity of nearby neurons, although the identity of these cells is relatively unknown, especially for those underlying the generation of inhibitory synaptic events. To address these fundamental questions, we developed an in vitro submerged slice preparation of the mouse entorhinal cortex that generates robust and regular spontaneous recurrent network activity in the form of the slow oscillation. By performing whole-cell recordings from multiple cell types identified with green fluorescent protein expression and electrophysiological and/or morphological properties, we show that distinct functional subpopulations of neurons exist in the entorhinal cortex, with large variations in contribution to the generation of balanced excitation and inhibition during the slow oscillation. The most active neurons during the slow oscillation are excitatory pyramidal and inhibitory fast spiking interneurons, receiving robust barrages of both excitatory and inhibitory synaptic potentials. Weak action potential activity was observed in stellate excitatory neurons and somatostatin-containing interneurons. In contrast, interneurons containing neuropeptide Y, vasoactive intestinal peptide, or the 5-hydroxytryptamine (serotonin) 3a receptor, were silent. Our data demonstrate remarkable functional specificity in the interactions between different excitatory and inhibitory cortical neuronal subtypes, and suggest that it is the large recurrent interaction between pyramidal neurons and fast spiking interneurons that is responsible for the generation of persistent activity that characterizes the depolarized states of the cortex.

Time course and action spectrum of vibrotactile adaptation.

Abstract: In a series of experiments designed to explore the processes underlying adaptation of the sense of flutter-vibration, vibrotactile threshold was measured on the pad of the index finger, using Bekesy tracking. Unadapted thresholds were first measured, for a number of frequencies (4-90 Hz) and contactor sizes (1-8 mm diameter). As expected, these measurements indicated the presence of (1) a Pacinian system possessing spatial summation and increasing in sensitivity, as frequency was raised, at the rate of 12 dB/octave; and (2) a non-Pacinian system showing little spatial summation, and with a frequency characteristic matching that of the NP I mechanism of Bolanowski et al. (1988). These baseline data of Experiment 1 guided the selection of stimulus parameters for subsequent experiments, in which threshold for a test stimulus was measured before, during, and after periods of vibrotactile adaptation. In Experiment 2, test stimuli of 10 Hz and 50 Hz were combined factorially with 30-dB SL adapting stimuli of the same two frequencies. When the test stimulus was 10 Hz, the two adapting frequencies were equally effective in raising threshold; however, when the 50-Hz test stimulus was used, the 50-Hz adapting stimulus raised threshold by a greater amount than did the 10-Hz adapter. These results confirm on the finger the independence of adaptation in Pacinian and non-Pacinian channels, a result previously established on the thenar by other workers. For all four frequency combinations, threshold rose exponentially with a time constant of 1.5-2 min. In Experiment 3, an action spectrum was determined, showing the adapting amplitude needed at each of a series of frequencies to raise the threshold of a 10-Hz stimulus by 10 dB; this spectrum was essentially flat from 30 to 90 Hz. The results, taken in conjunction with what is known about rapidly adapting cutaneous mechanoreceptors, imply that the effectiveness of an adapting stimulus is not determined solely by the amount of activity it generates in first-order afferents.

Spatial Summation Can Explain the Attentional Modulation of Neuronal Responses to Multiple Stimuli in Area V4

Abstract: Although many studies have shown that the activity of individual neurons in a variety of visual areas is modulated by attention, a fundamental question remains unresolved: can attention alter the visual representations of individual neurons? One set of studies, primarily relying on the attentional modulations observed when a single stimulus is presented within the receptive field of a neuron, suggests that neuronal selectivities, such as orientation or direction tuning, are not fundamentally altered by attention (Salinas and Abbott, 1997; McAdams and Maunsell, 1999; Treue and Martinez Trujillo, 1999). Another set of studies, relying on modulations observed when multiple stimuli are presented within a receptive field, suggests that attention can alter the weighting of sensory inputs (Moran and Desimone, 1985; Luck et al., 1997; Reynolds et al., 1999; Chelazzi et al., 2001). In these studies, when preferred and nonpreferred stimuli are simultaneously presented, responses are much stronger when attention is directed to the preferred stimulus than when it is directed to the nonpreferred stimulus. In this study, we recorded neuronal responses from individual neurons in visual cortical area V4 to both single and paired stimuli with a variety of attentional allocations and stimulus combinations. For each neuron studied, we constructed a quantitative model of input summation and then tested various models of attention. In many neurons, we are able to explain neuronal responses across the entire range of stimuli and attentional allocations tested. Specifically, we are able to reconcile seemingly inconsistent observations of single and paired stimuli attentional modulation with a new model in which attention can facilitate or suppress specific inputs to a neuron but does not fundamentally alter the integration of these inputs.