Quantitative analyses of the effect of muscimol- and control PBS-injection on V1-activation.

<p>Data of the the injected (left) and non-injected (right) V1 are shown. (A, B) Muscimol reliably blocked both ipsilateral (A) and contralateral eye evoked activity in the left V1 (B), reduced ipsilateral but not contralateral eye evoked V1-activity in the right V1 (C, D), while PBS-injection in a control group of animals had no significant effect (E–H). Evoked responses shown as line plots from single animals (top; each line represents data from one animal before/after the muscimol- or PBS-injection, p of paired t-tests are given), bar plots with group averages (middle plots) and mediolateral profiles (bottom plots, X-axis in 150 pixels equaling 3600 µm) before (black) and after injection (red).</p

Interaction of Excitation and Inhibition in Anteroventral Cochlear Nucleus Neurons That Receive Large Endbulb Synaptic Endings

Spherical bushy cells (SBCs) of the anteroventral cochlear nucleus (AVCN) receive their main excitatory input from auditory nerve fibers (ANFs) through large synapses, endbulbs of Held. These cells are also the target of inhibitory inputs whose function is not well understood. The present study examines the role of inhibition in the encoding of low-frequency sounds in the gerbil's AVCN. The presynaptic action potentials of endbulb terminals and postsynaptic action potentials of SBCs were monitored simultaneously in extracellular single-unit recordings in vivo. An input–output analysis of presynaptic and postsynaptic activity was performed for both spontaneous and acoustically driven activity. Two-tone stimulation and neuropharmacological experiments allowed the effects of neuronal inhibition and cochlear suppression on SBC activity to be distinguished. Ninety-one percent of SBCs showed significant neuronal inhibition. Inhibitory sidebands enclosed the high- or low-frequency, or both, sides of the excitatory areas of these units; this was reflected as a presynaptic to postsynaptic increase in frequency selectivity of up to one octave. Inhibition also affected the level-dependent responses at the characteristic frequency. Although in all units the presynaptic recordings showed monotonic rate-level functions, this was the case in only half of the postsynaptic recordings. In the other half of SBCs, postsynaptic inhibitory areas overlapped the excitatory areas, resulting in nonmonotonic rate-level functions. The results demonstrate that the sound-evoked spike activity of SBCs reflects the integration of acoustically driven excitatory and inhibitory input. The inhibition specifically affects the processing of the spectral, temporal, and intensity cues of acoustic signals

Cluster analyses considering all evaluated response properties.

<p><b>A</b>: Dendrogram illustrating the result of hierarchical cluster analysis. The units (n = 233) are lined up at the bottom of the graph. The analysis suggests five clusters characterized by a specific distribution of parameter values. <b>B</b>: Mean of the respective parameter values for each property in the resulted clusters I–V. The values are standardized and normalized to the respective maxima (for original data and statistical analyses see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029965#pone-0029965-t002" target="_blank">table 2</a>). Note that for almost all individual properties significant differences exist between the clusters, and some properties also correlated across clusters. <b>C</b>: However, principal component analysis gives no indication for clearly separated groups of units, neither for the different clusters gathered from hierarchical cluster analysis (<b>C1</b>) nor for the different PSTH types (<b>C2</b>). In both cases units establishing different groups tend to accumulate in different regions of the plot. Still, the different groups strongly overlap, especially in the centre of the plot. Thus, with respect to their physiological properties the AVCN neurons form a continuum rather than distinct groups.</p

Waveform analysis.

<p><b>A1–A4</b>: Averaged and normalized waveforms of single units sorted according to their PSTH types (numbers of units indicated in the graphs). The inset in A1 shows the mean waveform of the action potentials (black line, grey lines: S.D.) of a PL unit displaying the presynaptic component P and the two postsynaptic components ‘A’ and ‘B’. <b>B1</b>: Normalized average waveforms of all units of the respective PSTH types. <b>C1</b>: Signal-to-noise ratio and <b>C2</b>: duration from the maximum to the minimum of the waveforms of the respective PSTH types. Each symbol represents the value of a single AVCN unit. Significant differences (p≤0.05) between PSTH types are indicated with asterisks.</p

Cluster analyses based on a restricted set of parameters.

<p>See text for the reasons of the restriction. The parameter considered are indicated in B. Design of the graphs is the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029965#pone-0029965-g006" target="_blank">figure 6</a>. <b>A</b>: The present cluster analysis suggests a distinction of four clusters (a–d) with <b>B</b>: specific properties. Note that there is some correspondence between this restricted analysis and the analysis given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029965#pone-0029965-g006" target="_blank">figure 6:</a> Cluster ‘a’ relates to cluster V; ‘b’ to I, ‘c’ to II, and ‘d’ to IV. <b>C</b>: The principal component analysis arranges the units in one big coherent cluster. Units establishing different clusters (<b>C1</b>) and different PSTH types (<b>C2</b>) still could not be separated.</p

Responses to SAM.

<p>Synchronization indices (left column) and entrainment (right column) as a function of modulation frequency for the different PSTH types. The respective bottommost plots show the average transfer functions for each PSTH type. The horizontal line indicates the 0.3 cut-off criterion that was chosen to classify responses as being phase-locked. Note that C_S units show best and PL units worst ability to comodulate with fast fluctuations in stimulus amplitude.</p

Physiological response properties of different PSTH groups in AVCN.

<p>abbreviations explained in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029965#s2" target="_blank">methods</a>.</p><p>categorical values are described in text.</p>a<p>Means ± S.D./Median (25%, 75%).</p>b<p>PSTH groups that do not significantly differ are within one parentheses.</p

Principal component analysis employing three principal components and recheck of PSTH classification.

<p>Same sample of units (n = 174) and analysis as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029965#pone-0029965-g007" target="_blank">figure 7</a>. <b>A1</b>: Principal component analysis with assignment of the units to the different clusters gathered from hierarchical cluster analysis. <b>A2</b>: Principal component analysis with assignment of the units to the different PSTH types. Note that even a visualization based on the three dominant principal components does not indicate a clear separation of unit types. <b>B</b>: PSTHs of units in regions of the plot which are mainly occupied by other PSTH types, i.e. a PL_N (<b>B1</b>), a C_S (<b>B2</b>) and a unit which is not unambiguously to classify (<b>B3</b>). This unit was classified as C_T, but it could also be a PL.</p

Physiological response properties of different clusters of AVCN units according to hierarchical cluster analysis using all evaluated properties.

<p>abbreviations explained in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029965#s2" target="_blank">methods</a>.</p><p>categorical values are described in text.</p>a<p>Means ± S.D./Median (25%, 75%).</p>b<p>cluster that do not significantly differ are within one parentheses.</p

Classification of AVCN units based on PSTH types.

<p><b>A1–A4</b>: Response patterns during tone burst stimulation (100 ms, 80 dB SPL at CF) of four units; dot raster to 50 stimulus presentations above, PSTH below (bin width 0.5 ms). <b>A1</b>: <i>primary-like</i> (PL), <b>A2</b>: <i>primary-like with notch</i> (PL_N), <b>A3</b>: <i>transient chopper</i> (C_T), <b>A4</b>: <i>sustained chopper</i> (C_S). The insets show the inter-spike interval (ISI) distribution during the first 20 ms of the stimulus of the respective units (bin width 0.1 ms); <b>B1</b>: Relation between mean ISI and S.D. of ISI for the different unit types (symbols as indicated in the figure) <b>B2</b>: Relation between the first spike latency (FSL) and the jitter of the FSL. Note that both types of <i>chopper</i> units have lower ISIs and a lower variation in ISI than PL and PL_N units. Shortest latencies are observed in PL_N units.</p