Biomedical subjects

Kenneth E Hancock

Publications and source records attributed to Kenneth E Hancock.

3 recordsLinked to original sources

PubMed2004

A physiologically based model of interaural time difference discrimination.

Interaural time difference (ITD) is a cue to the location of sounds containing low frequencies and is represented in the inferior colliculus (IC) by cells that respond maximally at a particular best delay (BD). Previous studies have demonstrated that single ITD-sensitive cells contain sufficient information in their discharge patterns to account for ITD acuity on the midline (ITD = 0). If ITD discrimination were based on the activity of the most sensitive cell available ("lower envelope hypothesis"), then ITD acuity should be relatively constant as a function of ITD. In response to broadband noise, however, the ITD acuity of human listeners degrades as ITD increases. To account for these results, we hypothesize that pooling of information across neurons is an essential component of ITD discrimination. This report describes a neural pooling model of ITD discrimination based on the response properties of ITD-sensitive cells in the IC of anesthetized cats. Rate versus ITD curves were fit with a cross-correlation model of ITD sensitivity, and the parameters were used to constrain a population model of ITD discrimination. The model accurately predicts ITD acuity as a function of ITD for broadband noise stimuli when responses are pooled across best frequency (BF). Furthermore, ITD tuning based solely on a system of internal delays is not sufficient to predict ITD acuity in response to 500 Hz tones, suggesting that acuity is likely refined by additional mechanisms. The physiological data confirms evidence from the guinea pig that BD varies systematically with BF, generalizing the observation across species.

Acoustic Stimulation↗

PubMed2002

Intracellularly labeled fusiform cells in dorsal cochlear nucleus of the gerbil. I. Physiological response properties.

Fusiform cells in the dorsal cochlear nucleus (DCN) of barbiturate-anesthetized Mongolian gerbils were characterized physiologically and labeled with neurobiotin. This report is based on 17 fusiform cells for which there was reasonable confidence in the association between physiological data and recovered anatomy. The qualitative morphology of these cells was no different from that reported in previous studies. The acoustic response properties were generally consistent with those described in the barbiturate-anesthetized cat. Most responses were of the pauser or buildup type, but a dependence on stimulus frequency and intensity was observed. Stimulus-evoked sustained depolarizations and large, long-lasting afterhyperpolarizations were common membrane potential features. The cells in this study showed a greater tendency to discharge regularly than did those of the cat, likely as a result of the longer interstimulus interval used. Barbiturate anesthesia appears to mask an interspecies difference in DCN physiology that is apparent in unanesthetized, decerebrate preparations. The response of these fusiform cells to a depolarizing current pulse could be altered by the presence of a hyperpolarizing prepulse. Buildup, pauser, and chopper patterns could each be created using appropriate combinations of hyperpolarizing and depolarizing pulse amplitudes. Thus the adult gerbil appears to express the inactivating potassium conductance previously shown to affect fusiform cell firing patterns in vitro. The results further demonstrate that the effects of these potassium currents are readily observed in vivo. Finally, the fusiform cells in this study were quite variable with respect to a number of response properties, including the resting potential, input resistance, spontaneous activity, relative noise index, normalized tone slope, and regularity histogram shape. This diversity likely results from cell-to-cell variations in the balance of activity within the relatively complex network to which the fusiform cells belong, although effects of impalement may contribute to the extent of the diversity.

Acoustic Stimulation↗

PubMed2002

Intracellularly labeled fusiform cells in dorsal cochlear nucleus of the gerbil. II. Comparison of physiology and anatomy.

Fusiform cells represent the major class of dorsal cochlear nucleus (DCN) projection neuron. Although much is understood about their physiology and anatomy, there remain unexplored issues with important functional implications. These include interspecies differences in DCN physiology and the nature of the cell-to-cell variations in fusiform cell physiology. To address these issues, a quantitative examination was made of the physiology and anatomy of 17 fusiform cells from a companion study. The results suggest that the basal dendrites of gerbil fusiform cells may be electrotonically more compact than those of the cat. This relative decrease in the filtering of excitatory inputs might account for the lower incidence of type IV units in that species. These data also suggest that the gerbil DCN lacks the high-frequency specialization described in the cat, because the tonotopic arrangement of the gerbil fusiform cells quantitatively matches the place-frequency map for the gerbil cochlea. Certain physiological properties have anatomical correlates. First, the basal dendrites of low spontaneous rate cells are directed away from the soma only in the caudal direction, while the high spontaneous rate cells have basal dendrites extending rostrally and caudally. Second, input resistance was dominated by the surface area of the apical dendrite. Third, the discharge pattern was correlated with apical dendrite orientation. Finally, there was a spatial gradient of sensitivity to broadband noise organized at least partially within an isofrequency axis. Such trends indicate that neighboring fusiform cells are endowed with different signal processing capabilities.

Animals↗