Novel Space Alters Theta and Gamma Synchrony Across the Longitudinal Axis of the Hippocampus.

Hippocampal theta (6–10 Hz) and gamma (25–50 Hz and 65–100 Hz) local field potentials (LFPs) reflect the dynamic synchronization evoked by inputs impinging upon hippocampal neurons. Novel experience is known to engage hippocampal physiology and promote successful encoding. Does novelty synchronize or desynchronize theta and/or gamma frequency inputs across the septotemporal (long) axis of the hippocampus (HPC)? The present study tested the hypothesis that a novel spatial environment would alter theta power and coherence across the long axis. We compared theta and gamma LFP signals at individual (power) and millimeter distant electrode pairs (coherence) within the dentate gyrus (DG) and CA1 region while rats navigated a runway (1) in a familiar environment, (2) with a modified path in the same environment and (3) in a novel space. Locomotion in novel space was related to increases in theta and gamma power at most CA1 and DG sites. The increase in theta and gamma power was concurrent with an increase in theta and gamma coherence across the long axis of CA1; however, there was a significant decrease in theta coherence across the long axis of the DG. These findings illustrate significant shifts in the synchrony of entorhinal, CA3 and/or neuromodulatory afferents conveying novel spatial information to the dendritic fields of CA1 and DG targets across the long axis of the HPC. This shift suggests that the entire theta/gamma-related input to the CA1 network, and likely output, receives and conveys a more coherent message in response to novel sensory experience. Such may contribute to the successful encoding of novel sensory experience

Analysis of situational leadership styles of principals of more effective elementary schools in Connecticut

The purpose of this study was to investigate and analyze the behavior patterns that principals in the Connecticut School Effectiveness Project exhibit when they attempt to lead the staff into developing a more instructionally effective school. The leadership analysis was based on Hersey and Blanchard\u27s Situational Leadership Theory and on an ethnographic analysis of the leader\u27s management roles.^ The following three statistical hypotheses were developed for the purpose of this study: (Ho1) There is no significant difference between principals of schools with high and low effectiveness ratings and their: (1.1) Instructional Leadership scores in the C.S.E.Q. (1.2) Adaptability scores on the L.E.A.D. (1.3) Style Frequency on the L.E.A.D. (Ho2) There is no significant difference between the principals of schools with high and low effectiveness ratings and their self perceptions of their leadership style as well as the perceptions of their staff of their leadership style. (Ho3) There is no significant interaction between the schools\u27 effectiveness ratings and the adaptability of principals as measured by their self perception and the perceptions of their professional staffs.^ The data was analyzed using the ANOVA statistical procedure at p $\u3c$.05 level of significance. The statistical and ethnographic analysis revealed the following findings: (1) More effective instructional leaders tend to manage more effective schools; (2) There is no best leadership style for all situations. (3) Principals assume different leadership styles depending on the situation. (4) The primary leadership style used by principals participating in the effective schools is coaching; (5) Principals that perceive themselves as being more participating leaders manage more effective schools. (6) The managerial behavior of principals is diverse and fragmented; (7) Due to the diversity of roles assumed by principals and due to the fragmented nature of their work, this study strongly suggests that principals that are able to vary their leadership style in accordance with the situation, are more effective leaders.^ This study revealed information that will enhance the Connecticut School Effectiveness Project\u27s staffs ability to plan and implement effective short and long term strategies that will help schools develop a more effective instructional program.

Analysis of situational leadership styles of principals of more effective elementary schools in Connecticut

The purpose of this study was to investigate and analyze the behavior patterns that principals in the Connecticut School Effectiveness Project exhibit when they attempt to lead the staff into developing a more instructionally effective school. The leadership analysis was based on Hersey and Blanchard\u27s Situational Leadership Theory and on an ethnographic analysis of the leader\u27s management roles.^ The following three statistical hypotheses were developed for the purpose of this study: (Ho1) There is no significant difference between principals of schools with high and low effectiveness ratings and their: (1.1) Instructional Leadership scores in the C.S.E.Q. (1.2) Adaptability scores on the L.E.A.D. (1.3) Style Frequency on the L.E.A.D. (Ho2) There is no significant difference between the principals of schools with high and low effectiveness ratings and their self perceptions of their leadership style as well as the perceptions of their staff of their leadership style. (Ho3) There is no significant interaction between the schools\u27 effectiveness ratings and the adaptability of principals as measured by their self perception and the perceptions of their professional staffs.^ The data was analyzed using the ANOVA statistical procedure at p $\u3c$.05 level of significance. The statistical and ethnographic analysis revealed the following findings: (1) More effective instructional leaders tend to manage more effective schools; (2) There is no best leadership style for all situations. (3) Principals assume different leadership styles depending on the situation. (4) The primary leadership style used by principals participating in the effective schools is coaching; (5) Principals that perceive themselves as being more participating leaders manage more effective schools. (6) The managerial behavior of principals is diverse and fragmented; (7) Due to the diversity of roles assumed by principals and due to the fragmented nature of their work, this study strongly suggests that principals that are able to vary their leadership style in accordance with the situation, are more effective leaders.^ This study revealed information that will enhance the Connecticut School Effectiveness Project\u27s staffs ability to plan and implement effective short and long term strategies that will help schools develop a more effective instructional program.

Spiking network optimized for word recognition in noise predicts auditory system hierarchy

The auditory neural code is resilient to acoustic variability and capable of recognizing sounds amongst competing sound sources, yet, the transformations enabling noise robust abilities are largely unknown. We report that a hierarchical spiking neural network (HSNN) optimized to maximize word recognition accuracy in noise and multiple talkers predicts organizational hierarchy of the ascending auditory pathway. Comparisons with data from auditory nerve, midbrain, thalamus and cortex reveals that the optimal HSSN predicts several transformations of the ascending auditory pathway including a sequential loss of temporal resolution and synchronization ability, increasing sparseness, and selectivity. The optimal organizational scheme enhances performance by selectively filtering out noise and fast temporal cues such as voicing periodicity, that are not directly relevant to the word recognition task. An identical network arranged to enable high information transfer fails to predict auditory pathway organization and has substantially poorer performance. Furthermore, conventional single-layer linear and nonlinear receptive field networks that capture the overall feature extraction of the HSNN fail to achieve similar performance. The findings suggest that the auditory pathway hierarchy and its sequential nonlinear feature extraction computations enhance relevant cues while removing non-informative sources of noise, thus enhancing the representation of sounds in noise impoverished conditions. Author summary: The brain\u27s ability to recognize sounds in the presence of competing sounds or background noise is essential for everyday hearing tasks. How the brain accomplishes noise resiliency, however, is poorly understood. Using neural recordings from the ascending auditory pathway and an auditory spiking network model trained for sound recognition in noise we explore the computational strategies that enable noise robustness. Our results suggest that the hierarchical feature organization of the ascending auditory pathway and the resulting computations are critical for sound recognition in the presence of noise

Theta Dynamics in Rat: Speed and Acceleration across the Septotemporal Axis

Theta (6–12 Hz) rhythmicity in the local field potential (LFP) reflects a clocking mechanism that brings physically isolated neurons together in time, allowing for the integration and segregation of distributed cell assemblies. Variation in the theta signal has been linked to locomotor speed, sensorimotor integration as well as cognitive processing. Previously, we have characterized the relationship between locomotor speed and theta power and how that relationship varies across the septotemporal (long) axis of the hippocampus (HPC). The current study investigated the relationship between whole body acceleration, deceleration and theta indices at CA1 and dentate gyrus (DG) sites along the septotemporal axis of the HPC in rats. Results indicate that whole body acceleration and deceleration predicts a significant amount of variability in the theta signal beyond variation in locomotor speed. Furthermore, deceleration was more predictive of variation in theta amplitude as compared to acceleration as rats traversed a linear track. Such findings highlight key variables that systematically predict the variability in the theta signal across the long axis of the HPC. A better understanding of the relative contribution of these quantifiable variables and their variation as a function of experience and environmental conditions should facilitate our understanding of the relationship between theta and sensorimotor/cognitive functions

Relationship between acceleration, deceleration and theta amplitude.

<p><b>A</b>: two-dimensional histograms for the relationship between deceleration and theta amplitude, with corresponding filtered theta, speed and acceleration traces for simultaneously recorded CA1 electrodes. All theta envelope units = ×10⁻⁴; all count units = ×10³. <b>B</b>: Electrodes were grouped according to septotemporal position. Mean partial correlation coefficients (controlling for speed) are shown for the relationship between deceleration (blue bar) and theta amplitude as well as for acceleration (red bar) and theta amplitude for CA1. As can be seen, when acceleration is separated into its positive and negative constituents, a differential relationship emerges such that deceleration is more predictive of theta amplitude as compared to acceleration. Theta amplitude was significantly modulated by both acceleration and deceleration across the entirety of the hippocampus for CA1. Additionally, deceleration explained more of the variability in theta amplitude across the entirety of CA1 axis. <b>C</b>: Partial correlation coefficients for the relationship between deceleration and theta amplitude (blue circles) and acceleration and theta amplitude (red circles) as a function of distance from the septal pole for CA1. Each dot represents the partial correlation coefficient between each index (acceleration, deceleration) and theta amplitude plotted as a function of distance from the septal pole. The relationship between deceleration and theta amplitude decreased across the septotemporal axis of CA1. <b>D</b>: Same as A, but for DG. Theta amplitude was significantly modulated by both acceleration and deceleration at septal and midseptotemporal DG sites. Further, deceleration explained more of the variability in theta amplitude than acceleration at DG sites.</p

Electrode locations, corresponding theta traces & relationship between theta amplitude and speed/acceleration/deceleration.

<p><b>A</b>: Flatmap representation of the hippocampal formation. Electrode placements are indicated as red dots. Each contour line represents a coronal section. Orange star denotes DG electrode as in B–D (bottom), while black star denotes CA1 electrode as in B–D (top). <b>B (top)</b>: Photomicrographs of a representative recording site in septal CA1. Middle photomicrograph shows a close-up (20×) of electrode tip, as denoted by the black arrow. The right photomicrograph depicts the next coronal section for verification that the electrode tract ends. The septal CA1 tract ends in slm. The raw, unfiltered LFP for representative CA1 slm electrode is shown. <b>B (bottom)</b>: Same as top (CA1), but for DG. The septal DG tract ends in the gcl. Theta trace for representative DG gcl electrode is shown. <b>C</b>: two-dimensional histogram (density plot) of the relationship between speed and theta amplitude for representative CA1 slm and DG gcl electrodes, as well as speed signal with overlaid theta trace. <b>D</b>: two-dimensional histograms for the relationship between theta amplitude and acceleration/deceleration for the same CA1 slm and DG gcl electrodes (all theta envelope units in 2D histograms = ×10⁻⁴; all count units = ×10³; all <i>p</i>-values<.0001). <b><i>Abbreviations</i></b>: sr = stratum radiatum; slm = stratum lacunosum moleculare; mol = molecular layer; gcl = granule cell layer.</p