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.

Hippocampal inhibitory neuron activity in the elevated potassium model of epilepsy

Abstract: 1. Whole cell patch-clamp recordings were made from CA1 stratum oriens inhibitory neurons of rat hippocampal slices in vitro to determine their contribution to the epileptiform activity elicited by elevating the extracellular potassium ion concentration ([K+]o) from 3.5 to 8.5 mM. 2. Under current-clamp conditions, spontaneous action potential activity in inhibitory neurons normally occurs in a sustained repetitive firing mode paced by nonsynaptic, intrinsic mechanisms. On elevation of [K+]o to 8.5 mM the pattern of activity is altered such that clusters of action potentials occur interrupted by periods of silence without an appreciable after hyperpolarization (AHP). In addition, elevation of [K+]o caused a large reduction in the action potential AHP amplitude and duration concomitant with a 20-mV shift in the reversal potential of the AHP. 3. In voltage clamp a small persistent inward current was observed after the introduction of elevated potassium concomitant with an increase in the frequency of spontaneous excitatory post-synaptic currents (EPSCs) in all interneurons studied. After a short period of time (approximately 1 min) temporal summation of synchronously occurring EPSCs contributed a periodic inward current (PIC; 10-40 pA, 0.8 Hz) that persisted for the duration of the [K+]o elevation. Analysis of the charge transfer associated with the PIC suggests that they comprise the temporal summation of approximately 35 EPSCs. This PIC was synchronous with the extracellular field potential recorded from the CA1 pyramidal neuron layer. 4. The PIC was responsible for the clustering of action potential activity because blockade of EPSC activity by the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) abolished PICs and reverted action potential activity to single sustained firing, despite the continued application of 8.5 mM [K+]o. Antagonists of N-methyl-D-aspartate receptors were without effect on either the PICs or the action potential activity. 5. Addition of the metabotropic glutamate receptor (mGluR) antagonist (+)-2-methyl-4-carboxyphenylglycine (MCPG) reversibly abolished the PIC without affecting the increase in EPSC frequency. 6. Recordings from CA3 pyramidal neurons in 8.5 mM [K+]o demonstrated that interictal activity occurred at a frequency identical to the PICs observed in interneurons. Interictal activity in CA3 pyramidal neurons was attenuated but never abolished by MCPG, suggesting a role for mGluR receptors in the maintenance of interictal activity in area CA3.(ABSTRACT TRUNCATED AT 400 WORDS)

Dendritic Ih selectively blocks temporal summation of unsynchronized distal inputs in CA1 pyramidal neurons.

Abstract: The active dendritic conductances shape the input-output properties of many principal neurons in different brain regions, and the various ways in which they regulate neuronal excitability need to be investigated to better understand their functional consequences. Using a realistic model of a hippocampal CA1 pyramidal neuron, we show a major role for the hyperpolarization-activated current, Ih, in regulating the spike probability of a neuron when independent synaptic inputs are activated with different degrees of synchronization and at different distances from the soma. The results allowed us to make the experimentally testable prediction that the Ih in these neurons is needed to reduce neuronal excitability selectively for distal unsynchronized, but not for synchronized, inputs.

Information-Processing Channels in the Tactile Sensory System: A Psychophysical and Physiological Analysis

Abstract: Channels in touch -- Identification of specific neural systems responsible for mechanoreception -- Duplex model of mechanoreception -- Spatial and temporal summation in the P system -- The neural bases of the tactile systems -- Anatomy of tactile receptors -- Neurophysiology of tactile receptors and their nerve fibers -- Neural bases of the P and NP systems -- Four neural systems mediate the detection of vibratory stimuli -- Frequency selectivity of a neural system is determined by its receptors -- From neural systems to information-processing channels -- Sensation-magnitude enhancement occurs within but not across channels -- Multichannel model of tactile sensitivity -- The psychophysical tuning curve -- Testing the multichannel model through experiments on adaptation and masking -- Adaptation reveals the existence of tactile channels -- Masking occurs within but not across channels -- Testing the multichannel model through experiments on sensory learning -- Properties of tactile channels -- The frequency selectivity of channels -- Temporal summation and temporal acuity -- Spatial acuity -- Edge detection -- Spatial summation -- Effects of observer characteristics -- Effects of aging on the sensitivity of tactile channels -- Effects of the menstrual cycle -- The functional roles of channels -- Channels enhance the detectability of stimuli -- Channels enhance the discriminability of stimuli -- The functional roles of the individual tactile channels -- The decibel scale -- The functional role of the PC channel -- The functional role of the RA channel -- The functional role of the SA I channel -- The functional role of the SA II channel -- Specialization of channels -- Channel interactions -- Summation of sensation magnitude across channels -- The perception of texture -- Role of attention in the enhancement and summation of sensation magnitude -- Interactions between tactile channels and other somatosensory submodalities.