Biomedical subjects

Daniel B Polley

Publications and source records attributed to Daniel B Polley.

6 recordsLinked to original sources

PubMed2006

Perceptual learning directs auditory cortical map reorganization through top-down influences.

The primary sensory cortex is positioned at a confluence of bottom-up dedicated sensory inputs and top-down inputs related to higher-order sensory features, attentional state, and behavioral reinforcement. We tested whether topographic map plasticity in the adult primary auditory cortex and a secondary auditory area, the suprarhinal auditory field, was controlled by the statistics of bottom-up sensory inputs or by top-down task-dependent influences. Rats were trained to attend to independent parameters, either frequency or intensity, within an identical set of auditory stimuli, allowing us to vary task demands while holding the bottom-up sensory inputs constant. We observed a clear double-dissociation in map plasticity in both cortical fields. Rats trained to attend to frequency cues exhibited an expanded representation of the target frequency range within the tonotopic map but no change in sound intensity encoding compared with controls. Rats trained to attend to intensity cues expressed an increased proportion of nonmonotonic intensity response profiles preferentially tuned to the target intensity range but no change in tonotopic map organization relative to controls. The degree of topographic map plasticity within the task-relevant stimulus dimension was correlated with the degree of perceptual learning for rats in both tasks. These data suggest that enduring receptive field plasticity in the adult auditory cortex may be shaped by task-specific top-down inputs that interact with bottom-up sensory inputs and reinforcement-based neuromodulator release. Top-down inputs might confer the selectivity necessary to modify a single feature representation without affecting other spatially organized feature representations embedded within the same neural circuitry.

Acoustic Stimulation↗

PubMed2006

Severe hearing loss in Dlxl mutant mice.

The Dlx homeobox gene family participates in regulating middle and inner ear development. A significant role for Dlxl, in particular,has been demonstrated in the development of the middle ear ossicles, but the functional consequences of Dlx.l gene mutation on hearing thresholds has not been assessed. The present study characterizes auditory brainstem responses to click and tonal stimuli in a non-lethal variant of a Dlxl gene knockout. We found that peripheral hearing thresholds for click and tonal stimuli were significantly elevated in homozygous Dlxl knockout (Dlxl-/ ) compared to both heterozygous (Dlxl+/ ) and wild type (Dlxl+/+) mice. Thus, abnormal mor-phogenesis of the incus and stapes that has been documented previously with histological measures is now known to result in a severe peripheral hearing deficit.

Animals↗

PubMed2005

Fine functional organization of auditory cortex revealed by Fourier optical imaging.

We provide an overall view of the functional tonotopic organization of the auditory cortex in the rat. We apply a recently developed technique for acquiring intrinsic signal optical maps, Fourier imaging, in the rat auditory cortex. These highly detailed maps, derived in a several-minute-long recording procedure, delineate multiple auditory cortical areas and demonstrate their shapes, sizes, and tonotopic order. Beyond the primary auditory cortex, there are at least three distinct areas with fine-scale tonotopic organization, as well as at least one additional high-frequency field. The arrangement of all of these cortical areas is consistent across subjects. The accuracy of these optical maps was confirmed by microelectrode mapping in the same subjects. This imaging method allows fast mapping of the auditory cortex at high spatial resolution comparable to that provided by conventional microelectrode technique. Although spiking activity is largely responsible for the evoked intrinsic signals, certain features of the optical signal cannot be explained by spiking activity only, and should probably be attributed to other mechanisms inducing metabolic activity, such as subthreshold membrane phenomena.

Animals↗

PubMed2005

Whisker-based discrimination of object orientation determined with a rapid training paradigm.

Rats use their large facial whiskers to discriminate the spatial features of objects. Despite numerous electrophysiological recording studies in the central trigeminal whisker representations that document neurons tuned to the direction of whisker deflection, there is no behavioral evidence to date that rats can use their whiskers to discriminate between object orientations. In the present study, we characterized whisker-dependent orientation discrimination using a one-trial learning procedure. Sprague-Dawley rats were trained and tested in a three-arm 'Y-maze' that was outfitted with 180 independently moveable bars that protruded into the arms of the maze to contact the whiskers. On the first day, the maze was configured to have two arms with only horizontal bars and a third arm with only vertical bars and rats were allowed to freely explore all arms. On the second day, rats were isolated in one arm that contained only vertical bars as a conditioned stimulus (CS) and administered three mild foot shocks. On the third day, the maze was configured identically to the first day and rats were once again allowed to freely explore the maze. We measured the percentage of time spent in each arm of the maze and found that most rats spent significantly less time in the arm containing the CS after training compared to before training. Subsequent control experiments determined that the conditioned avoidance was attributable to orientation cues, was caused by the association of the conditioned and unconditioned stimulus and was whisker-dependent. Avoidance behavior was significantly reduced when the difference between the conditioned and non-conditioned orientation difference was reduced to 45 degrees. Thus, rats can discriminate object orientation with their whiskers and an estimate of their discrimination thresholds can be rapidly acquired through the application of a one-trial learning paradigm.

Afferent Pathways↗

PubMed2004

Associative learning shapes the neural code for stimulus magnitude in primary auditory cortex.

Since the dawn of experimental psychology, researchers have sought an understanding of the fundamental relationship between the amplitude of sensory stimuli and the magnitudes of their perceptual representations. Contemporary theories support the view that magnitude is encoded by a linear increase in firing rate established in the primary afferent pathways. In the present study, we have investigated sound intensity coding in the rat primary auditory cortex (AI) and describe its plasticity by following paired stimulus reinforcement and instrumental conditioning paradigms. In trained animals, population-response strengths in AI became more strongly nonlinear with increasing stimulus intensity. Individual AI responses became selective to more restricted ranges of sound intensities and, as a population, represented a broader range of preferred sound levels. These experiments demonstrate that the representation of stimulus magnitude can be powerfully reshaped by associative learning processes and suggest that the code for sound intensity within AI can be derived from intensity-tuned neurons that change, rather than simply increase, their firing rates in proportion to increases in sound intensity.

Acoustic Stimulation↗

PubMed2004

Naturalistic experience transforms sensory maps in the adult cortex of caged animals.

Much of what is known about the functional organization and plasticity of adult sensory cortex is derived from animals housed in standard laboratory cages. Here we report that the transfer of adult rats reared in standard laboratory cages to a naturalistic habitat modifies the functional and morphological organization of the facial whisker representation in the somatosensory 'barrel' cortex. Cortical whisker representations, visualized with repeated intrinsic signal optical imaging in the same animals, contracted by 46% after four to six weeks of exposure to the naturalistic habitat. Acute, multi-site extracellular recordings demonstrated suppressed evoked neuronal responses and smaller, sharper constituent receptive fields in the upper cortical layers (II/III), but not in the thalamic recipient layer (IV), of rats with naturalistic experience. Morphological plasticity of the layer IV barrel field was observed, but on a substantially smaller scale than the functional plasticity. Thus, transferring animals to an environment that promotes the expression of natural, innate behaviours induces a large-scale functional refinement of cortical sensory maps.

Animals↗