ABSTRACT
The rat hippocampus and entorhinal cortex have been shown to possess neurons with place fields that modulate their firing properties under different behavioral contexts. Such context-dependent changes in neural activity are commonly studied through electrophysiological experiments in which a rat performs a continuous spatial alternation task on a T-maze. Previous research has analyzed context-based differential firing during this task by describing differences in the mean firing activity between left-turn and right-turn experimental trials. In this article, we develop qualitative and quantitative methods to characterize and compare changes in trial-to-trial firing rate variability for sets of experimental contexts. We apply these methods to cells in the CA1 region of hippocampus and in the dorsocaudal medial entorhinal cortex (dcMEC), characterizing the context-dependent differences in spiking activity during spatial alternation. We identify a subset of cells with context-dependent changes in firing rate variability. Additionally, we show that dcMEC populations encode turn direction uniformly throughout the T-maze stem, whereas CA1 populations encode context at major waypoints in the spatial trajectory. Our results suggest scenarios in which individual cells that sparsely provide information on turn direction might combine in the aggregate to produce a robust population encoding.
Subject(s)
Action Potentials , CA1 Region, Hippocampal/physiology , Entorhinal Cortex/physiology , Maze Learning/physiology , Neurons/physiology , Space Perception/physiology , Analysis of Variance , Animals , Microelectrodes , Models, Neurological , Rats , Rats, Long-Evans , Signal Processing, Computer-Assisted , Time FactorsABSTRACT
Whereas substantial recent evidence has suggested to some that the medial entorhinal cortexá (MEC) plays a specialized role in spatial navigation, here we present evidence consistent with a broader role of the MEC in memory. A consideration of evidence on the anatomy and functional roles of medial temporal cortical areas and the hippocampus, and evidence from recordings from MEC neurons in rats performing a spatial memory task, suggest that the MEC may process information about both spatial and temporal context in support of episodic memory.
Subject(s)
Entorhinal Cortex/physiology , Hippocampus/physiology , Memory/physiology , Nerve Net/physiology , Parahippocampal Gyrus/physiology , Animals , Entorhinal Cortex/cytology , Hippocampus/cytology , Humans , Models, Neurological , Nerve Net/cytology , Orientation/physiology , Parahippocampal Gyrus/cytology , Rats , Space Perception/physiology , Time Perception/physiologyABSTRACT
Hippocampal neuronal activity distinguishes separate events that share common elements. Here, we examined whether the capacity to disambiguate overlapping experiences is an exclusive feature of hippocampal processing or whether information processing one stage earlier in the hippocampal system also disambiguates common elements of distinct experiences. We compared the spatial firing patterns of neurons in the dorsocaudal medial entorhinal cortex (dcMEC) and hippocampal CA1 neurons in animals continuously alternating left-turn and right-turn routes through a T-maze. Neurons in the dcMEC more strongly distinguished left-turn from right-turn trials compared with CA1 neurons, whereas CA1 neurons more selectivity encoded places traversed within each route. These results indicate that dcMEC spatial firing patterns are experience dependent and reflect the mnemonic demands of a spatial memory task. Furthermore, the results suggest that neuronal populations in the dcMEC and CA1 differentially emphasize complementary aspects of spatial memory representations.
Subject(s)
Entorhinal Cortex/physiology , Maze Learning/physiology , Neurons/physiology , Action Potentials/physiology , Animals , Male , Rats , Rats, Long-EvansABSTRACT
The genetic and environmental contributions to the development of general cognitive ability throughout the first 16 years of life were examined using sibling data from the Colorado Adoption Project. Correlations were analyzed along with structural equation models to characterize the genetic and environmental influences on longitudinal stability and instability. Intraclass correlations reflected both considerable genetic influence at each age and modest shared environmental influence within and across ages. Modeling results suggested that genetic factors mediated phenotypic stability throughout this entire period, whereas most age-to-age instability appeared to be due to nonshared environmental influences.
