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<p> A detailed quantitative examination of fusiform cell physiology and anatomy was made in this study. The following findings<sup></sup>will be discussed. <em>1</em>) The basal dendrite in the gerbil is shorter<sup></sup>than in the cat. <em>2</em>) The gerbil DCN appears to lack the high-frequency<sup></sup>specialization of the cat DCN. <em>3</em>) High spontaneous firing rates<sup></sup>are correlated with basal dendrites having both rostrally and<sup></sup>caudally directed branches, while low spontaneous rates are correlated<sup></sup>with basal dendrites having only caudally directed branches. <em>4</em>)<sup></sup>The inhibition reflected in the slope of the regularity histogram<sup></sup>is related to the orientation of the apical arbor. <em>5</em>) Noise response<sup></sup>strength appears to be systemically organized within an isofrequency<sup></sup>sheet. </p> <p> <em>Consideration of the basal arbor total length</em> </p> <p> The basal dendrites in the gerbil have about 70% the total length that they do in the cat and thus may be electrotonically<sup></sup>more compact. The equivalent cylinder model for a dendritic arbor<sup></sup>has a characteristic electrotonic length, which is proportional<sup></sup>to the ratio of the physical length of the cylinder to the square<sup></sup>root of its diameter (Rall 1977<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B34"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). Consider a hypothetical cat<sup></sup>fusiform cell that has three primary basal dendrites giving rise<sup></sup>to identical branching structures. One possibility is that the<sup></sup>"gerbil" fusiform cell retains all three branches, but each branch<sup></sup>is shortened by a third. The equivalent cylinder for such a cell<sup></sup>would be physically shorter than its counterpart in the cat, but<sup></sup>have the same diameter and hence a shorter electrotonic length.<sup></sup>A gerbil fusiform cell could also be produced by removing one<sup></sup>of the three hypothetical branches, giving the observed one-third<sup></sup>reduction in total length. The equivalent cylinder would have<sup></sup>the same physical length as the cat fusiform cell, but its diameter<sup></sup>would be smaller, resulting in a longer electrotonic<sup></sup>length. </p> <p> Which case best represents the actual situation? Blackstad et al. did not report branch order statistics for the cat, so it<sup></sup>is not possible to make a comparison in this regard. But, as shown<sup></sup>in Table <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#T2">2</a>, the height of the basal arbor is about one-third<sup></sup>smaller in the gerbil than in the cat. This would seem to reject<sup></sup>the second scenario above, since the pruning of one branch would<sup></sup>not affect the size of the remaining branches and hence the arbor<sup></sup>height should remain about the same. This leaves the first scenario<sup></sup>as the most viable and suggests that the effect of dendritic shortening<sup></sup>in the gerbil is to make the basal arbor electrotonically more<sup></sup>compact than in the<sup></sup>cat. </p> <p> Assuming that inputs from the auditory nerve are distributed toward the distal ends of the basal dendrites (Smith and Rhode<sup></sup>1985<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B42"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>), a possible effect of this electrotonic shortening would<sup></sup>be to decrease the attenuation of excitatory synaptic potentials.<sup></sup>To the extent that inhibitory inputs are received at more proximal<sup></sup>locations (Berrebi and Mugnaini 1991<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B4"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>; Saint-Marie et al. 1991<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B40"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>),<sup></sup>they are relatively unaffected by the overall length of the dendrite.<sup></sup>Hence, an electrotonically more compact basal dendrite might preferentially<sup></sup>enhance excitatory drive relative to inhibition. Indeed, previous<sup></sup>results suggest that the proportion of DCN units having type IV<sup></sup>unit properties is smaller in the gerbil than in the cat (11%<sup></sup>vs. 32-45%) and the proportion of type III units is larger (62%<sup></sup>vs. 23%) (Davis et al. 1996<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B8"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). Ding et al. (1999)<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B10"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a> reported on 13<sup> </sup>labeled fusiform cells from the decerebrate gerbil, none of which<sup></sup>had classic type IV unit response properties. Interestingly, the<sup></sup>type IV unit incidence in rabbit (23%) and chinchilla (25%) appears<sup></sup>to follow the same size-related trend (Davis et al. 1996<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B8"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>; Hui<sup></sup>and Disterhoft 1980<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B14"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>; Kaltenbach and Saunders 1987<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B18"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). </p> <p> This species-related difference in unit incidence was considered by Davis and Voigt (1996)<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B9"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a> using a point neuron model. Their<sup></sup>hypothesis was that a weakened contingent of type II unit inhibition<sup></sup>onto DCN projection neurons was responsible for the lack of type<sup></sup>IV units found in the gerbil relative to the cat. They showed<sup></sup>that a 40-50% reduction in the number of type II unit inputs was<sup></sup>sufficient to turn a model type IV unit into a type IV-T or type<sup></sup>III unit. A hypothesis based on the present finding in regard<sup></sup>to basal dendrite length, in contrast, suggests that the balance<sup></sup>is shifted toward excitation by an enhancement of the excitatory<sup></sup>inputs, rather than by a reduction of the inhibitory inputs. These<sup></sup>issues might effectively be explored using a compartmental model<sup></sup>of a fusiform<sup></sup>cell. </p> <p> <em>Tonotopic organization of the gerbil DCN</em> </p> <p> The qualitative picture of tonotopy presented in Fig. <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F2">2</a> agrees well with the description of frequency organization in gerbil<sup></sup>DCN obtained using measurements of 2-deoxyglucose uptake (Ryan<sup></sup>et al. 1982<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B39"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). On a more quantitative basis, the fusiform cell<sup></sup>BFs were plotted in Fig. <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F3">3</a> as a function of the cell position<sup></sup>along the tonotopic axis. The data plotted in this manner correspond<sup></sup>well with the cochlea place-frequency map determined by Müller<sup></sup>(1996)<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B27"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a> in the Mongolian gerbil (Fig. <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F3">3</a>). Such quantitative correspondence<sup></sup>between frequency representation in the cochlea and tonotopic<sup></sup>organization in central auditory structures is frequently observed<sup></sup>(Müller 1990<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B26"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). </p> <p> A notable exception is the cat DCN, whose representation of the 8- to 30-kHz range is disproportionately larger than the representation<sup></sup>of the same frequency range in the cochlea (Spirou et al. 1993<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B43"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>).<sup></sup>The head-related transfer function (HRTF) in the cat contains<sup></sup>spectral notches that may serve as cues for determining sound<sup></sup>source elevation (Rice et al. 1992<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B38"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). These notches fall in the<sup></sup>8- to 30-kHz range, suggesting that the enhanced representation<sup></sup>of these frequencies in the cat DCN is a functional specialization<sup></sup>related to coding those particular spectral features (Spirou et<sup></sup>al. 1993<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B43"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). </p> <p> The place-frequency analysis shown in Fig. <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F3">3</a> is limited to the extent that it is a one-dimensional description of the tonotopy;<sup></sup>it does not consider variations in cell density or the possibility<sup></sup>of a two-dimensional frequency gradient. The comparison with the<sup></sup>cat data of Spirou et al. (1993)<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B43"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a> is appropriate insofar as the<sup></sup>cat data are also based on a one-dimensional frequency axis. That<sup></sup>study, however, was based on BF estimates made at finely spaced<sup></sup>locations from a large number of electrode tracks. Furthermore,<sup></sup>Spirou et al. (1993)<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B43"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a> accounted for variations in fusiform cell<sup></sup>density when drawing conclusions about BF representation in the<sup></sup>DCN. </p> <p> The present data therefore should be regarded as preliminary but appear to underscore the fact that the tonotopy of the gerbil<sup></sup>DCN (and cochlea) is largely devoted to a lower frequency range.<sup></sup>Frequencies below 10 kHz occupy about 60% of the length of both<sup></sup>structures, and no specialized frequency representation in the<sup></sup>gerbil DCN is apparent. It is currently unknown whether or not<sup></sup>the gerbil HRTF contains spectral elevation cues similar to those<sup></sup>identified in the cat HRTF. Measurements of the HRTF in gerbil<sup></sup>and a more detailed examination of frequency representation in<sup></sup>the DCN are essential to a comparative evaluation of DCN function<sup></sup>in the two<sup></sup>species. </p> <p> <em>Spontaneous rate</em> </p> <p> The results indicate that the disposition of the basal dendrites is correlated with spontaneous rate for the fusiform cells<sup></sup>with best frequencies less than 2 kHz. The basal dendrites of<sup></sup>low SR cells are directed away from the soma only in the caudal<sup></sup>direction, while the high SR cells have basal dendrite branches<sup></sup>extending both rostrally and caudally. The basal arbors of the<sup></sup>low SR units, relative to those of the high SR units, have more<sup></sup>caudally located centroids. It is important to note that this<sup></sup>observation is based on relative comparisons of basal arbor structure<sup></sup>among cells having similar orientations. No absolute metric was<sup></sup>found to allow for a global quantification of the relationship<sup></sup>between SR and basal dendrite position. It was thus necessary<sup></sup>to limit consideration to this BF range because of the general<sup></sup>shift in long axis orientation with rostral-caudal position (and<sup></sup>hence BF) and because there were not sufficient numbers in any<sup></sup>other frequency band for cell-to-cell comparisons to be<sup></sup>made. </p> <p> It is not immediately clear how the orientation of the basal dendrites may influence spontaneous activity. Liberman (1993)<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B23"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a><sup></sup>suggested that auditory nerve inputs to the cat DCN may be segregated<sup></sup>based on spontaneous rate, with the high SR fibers terminating<sup></sup>deeper in the nucleus than the low SR fibers. This appears to<sup></sup>be inconsistent with our results, since the rostrally directed<sup></sup>basal dendrites of the high SR fusiform cells tend to be more<sup></sup>shallow in depth than the caudally directed branches common to<sup></sup>both SR<sup></sup>groups. </p> <p> Another possibility is that the rostrally directed branches access some other set of inputs that modulate spontaneous activity.<sup></sup>It also may be that the orientation characteristic of the high<sup></sup>SR cells has electrotonic consequences that emphasize excitatory<sup></sup>inputs over inhibitory inputs. Regardless of the mechanism, the<sup></sup>results suggest that the distribution of fusiform cell spontaneous<sup></sup>activities is not entirely due to<sup></sup>happenstance. </p> <p> It is difficult to say what functional consequences may arise from having a subset of the fusiform cell population preferentially<sup></sup>receive low SR input. It has been suggested that low SR auditory<sup></sup>nerve fibers are recruited to improve intensity discrimination<sup></sup>at high sound levels or are useful for signal in noise problems<sup></sup>(Viemeister 1983<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B45"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). Extending such interpretations to the DCN is<sup></sup>problematic, because they are based on the fact that low SR AN<sup></sup>fibers typically have high acoustic thresholds (Liberman 1978<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B22"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>),<sup></sup>a trend not generally characteristic of DCN units. It has been<sup></sup>shown that low SR AN fibers better synchronize to AM tones (Joris<sup></sup>and Yin 1992<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B17"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>), but there remains disagreement over the general<sup></sup>suitability of DCN projection neurons for encoding such stimuli<sup></sup>(Joris and Smith 1998<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B16"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). </p> <p> <em>Shape of regularity histogram</em> </p> <p> For the fusiform cells in the 0- to 2-kHz band, a correlation was observed between the orientation of the apical dendritic<sup></sup>arbor, quantified by the rotation, <img src="http://jn.physiology.org/math/12pt/normal/phiv.gif" alt="phi"><sub>apical</sub>, about the long axis<sup></sup>yielding the narrowest projection of the arbor, and the shape<sup></sup>of the regularity histogram, as quantified by the slope, <em>m</em><sub>1</sub> (Fig.<sup></sup><a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F7">7</a>). The slope values <em>m</em><sub>1</sub> and <em>m</em><sub>2</sub> are obtained by simultaneously<sup></sup>fitting two lines to the interspike interval plot after omitting<sup></sup>the first bin. For the data of this study, the value of <em>m</em><sub>1</sub> appears<sup></sup>to be a more useful measure of inhibition than the monotonicity<sup></sup>of the BF rate-level curve, because the <em>m</em><sub>1</sub> values are more evenly<sup></sup>distributed over a wider interval. A positive value of <em>m</em><sub>1</sub> reflects<sup></sup>a rate trend similar to the underlying excitatory drive from auditory<sup></sup>nerve fibers and hence suggests relatively weak inhibitory input.<sup></sup>Negative values are taken as an indication of a relatively stronger<sup></sup>inhibitory<sup></sup>contribution. </p> <p> One interpretation of this result is that the apical dendrite orientation determines the cross-sectional area of the arbor<sup></sup>perpendicular to the trajectory of the parallel fibers and hence<sup></sup>affects the pattern of activity in the apical arbor. For example,<sup></sup>those presenting a narrow face to the parallel fiber network may<sup></sup>be more strongly influenced by inhibitory inputs from the cartwheel<sup></sup>cell population. Although cartwheel cells are known to be acoustically<sup></sup>responsive, their activity is relatively weak and of high threshold<sup></sup>(Ding et al. 1999<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B10"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>; Parham and Kim 1995<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B32"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>) and would not be expected<sup></sup>to account for the relatively strong inhibition represented by<sup></sup>negative values of <em>m</em><sub>1</sub>. </p> <p> A second possibility is that since the neurons represented in Fig. <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F7">7</a> come from the ventrolateral third of the nucleus, the<sup></sup>change in apical arbor orientation may result from curvature of<sup></sup>the strial axis in this region (Blackstad et al. 1984<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B5"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). In this<sup></sup>case, the variations in orientation and in slope <em>m</em><sub>1</sub> may, in fact,<sup></sup>be functions of position. That no such dependence was apparent<sup></sup>in our position data may indicate limitations in the accuracy<sup></sup>of mapping position across different tissue<sup></sup>samples. </p> <p> <em>Possible significance of physiology-morphology correlations</em> </p> <p> Figures <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F5">5-7</a> demonstrate that certain morphological features are correlated with specific physiological properties. The geometries<sup></sup>of the apical and basal arbors influence input resistance and<sup></sup>spontaneous activity, respectively, while some aspect of cell<sup></sup>orientation apparently contributes to the inhibition measured<sup></sup>in the regularity histogram. It is thus possible that fusiform<sup></sup>cells along the isofrequency axis have graded physiological properties,<sup></sup>and hence different signal processing characteristics. In this<sup></sup>way, the fusiform cell population might be capable of performing<sup></sup>different operations on the same set of<sup></sup>inputs. </p> <p> A chance example from the present study illustrates that significant morphological differences may indeed exist between nearby<sup></sup>cells. Figure <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F9">9</a> is a sagittal view of two fusiform cells, labeled<sup></sup>in a single electrode track, their cell bodies separated by less<sup></sup>than 10 µm. They were located in the caudal DCN, and hence, as<sup></sup>described earlier, their long axes have a rostral-to-caudal orientation.<sup></sup>The apical arbor of the black-colored neuron is sparser than that<sup></sup>of the gray-colored neuron. Furthermore, the two basal arbors<sup></sup>do not overlap completely, but follow slightly different trajectories.<sup></sup>The results of Fig. <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F9">9</a> support the notion that neighboring fusiform<sup></sup>cells might have markedly different morphologies. </p> <p> <em>Organization of sensitivity to broadband noise</em> </p> <p> The notion that the DCN contains a functional axis orthogonal to the frequency axis is suggested by anatomical features. First,<sup></sup>there is the network of parallel fibers oriented perpendicular<sup></sup>to the underlying auditory nerve fibers. If systematic variations<sup></sup>in activity within the parallel fiber network contribute to the<sup></sup>variations in fusiform cell physiology, then fusiform cell properties<sup></sup>might vary in a spatially dependent manner. Another anatomical<sup></sup>substrate for a second axis in the DCN is a progressive decrease<sup></sup>in the number of vertical cells in the dorsomedial direction within<sup></sup>the coronal plane (Lorente de Nó 1981<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B24"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). Since vertical cells<sup></sup>presumably inhibit fusiform cells, the magnitude of inhibitory<sup></sup>response features (tone slope, interspike interval slope, etc.)<sup></sup>should also decrease in the dorsomedial<sup></sup>direction. </p> <p> The results show that the relative noise index is negatively correlated with position in the ventrolateral to dorsomedial<sup></sup>direction (Fig. <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F8">8</a><em>A</em>). In other words, fusiform cell responses to<sup></sup>noise tend to become weaker in the same general direction in which<sup></sup>Lorente de Nó (1981)<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B24"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a> reported the vertical cell layer becoming<sup></sup>thinner. A decrease in the number of vertical cells, however,<sup></sup>represents a loss of inhibition and so cannot account for the<sup></sup>diminishing noise responses. The noise sensitivity of DCN principal<sup></sup>cells is thought to be shaped by a source of wideband inhibition,<sup></sup>possibly originating in the PVCN (Nelken and Young 1994<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B29"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). The<sup></sup>observed noise responses in the current study might be accounted<sup></sup>for by an increasing contribution of this inhibitory source in<sup></sup>the dorsomedial<sup></sup>direction. </p> <p> Earlier studies have identified two inhibitory components to the response maps of type IV units, as schematized in Fig. <a href="http://jn.physiology.org/cgi/content/full/87/5/2520#F10">10</a>.<sup></sup>The first arises from a band of type II units, centered below<sup></sup>the BF of the type IV unit (Voigt and Young 1990<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B47"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>), while the second<sup></sup>component, wideband inhibition, possibly arises from the PVCN<sup></sup>and is centered above the type IV unit BF (Nelken and Young 1994<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B29"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>;<sup></sup>Spirou and Young 1991<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B44"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>). This organization might be consistent<sup></sup>with wideband inhibitory input strengthening in the dorsomedial<sup></sup>direction, as suggested by the present results, and the vertical<sup></sup>cell layer thinning in the same direction, as described by Lorente<sup></sup>de Nó. If, for example, each type IV unit receives input from<sup></sup>a band of type II units (presumably vertical cells) centered spatially<sup></sup>on BF, then the resulting inhibitory band would have a lower BF<sup></sup>because the vertical cells are more dense in that direction. Similarly,<sup></sup>if the wideband inhibition is stronger in the dorsomedial direction,<sup></sup>inhibition from a band spatially centered on BF will itself have<sup></sup>a higher BF. The idea that these two inhibitory sources might<sup></sup>trade for one another across the width of the DCN is consistent<sup></sup>with data presented by Nelken and Young (1994)<a href="http://jn.physiology.org/cgi/content/full/87/5/2520#B29"><img src="http://jn.physiology.org/icons/ref-arrow.gif" alt="ref-arrow.gif"></a>. Their Fig. 8<em>B</em><sup></sup>suggests that the influence of inhibition by type II units, as<sup></sup>measured by the maximum driven BF rate, is negatively correlated<sup></sup>with the influence of wideband inhibition, as measured by the<sup></sup>minimum inhibitory notch width. </p> <p> <em>Conclusion</em> </p> <p> This report has described differences between cats and gerbils in the anatomical properties of DCN fusiform cells and in their<sup></sup>tonotopic arrangement. The report also described systematic distributions<sup></sup>of functional properties within the fusiform cell population.<sup></sup>How such variations contribute to DCN function is yet to be<sup></sup>understood. </p> <p> </p> <p> </p>
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