Biomedical subjects

Sonja B Hofer

Publications and source records attributed to Sonja B Hofer.

4 recordsLinked to original sources

PubMed2006

Lifelong learning: ocular dominance plasticity in mouse visual cortex.

Ocular dominance plasticity has long served as a successful model for examining how cortical circuits are shaped by experience. In this paradigm, altered retinal activity caused by unilateral eye-lid closure leads to dramatic shifts in the binocular response properties of neurons in the visual cortex. Much of the recent progress in identifying the cellular and molecular mechanisms underlying ocular dominance plasticity has been achieved by using the mouse as a model system. In this species, monocular deprivation initiated in adulthood also causes robust ocular dominance shifts. Research on ocular dominance plasticity in the mouse is starting to provide insight into which factors mediate and influence cortical plasticity in juvenile and adult animals.

Animals↗

PubMed2005

Prior experience enhances plasticity in adult visual cortex.

The brain has a remarkable capacity to adapt to alterations in its sensory environment, which is normally much more pronounced in juvenile animals. Here we show that in adult mice, the ability to adapt to changes can be improved profoundly if the mouse has already experienced a similar change in its sensory environment earlier in life. Using the standard model for sensory plasticity in mouse visual cortex-ocular dominance (OD) plasticity-we found that a transient shift in OD, induced by monocular deprivation (MD) earlier in life, renders the adult visual cortex highly susceptible to subsequent MD many weeks later. Irrespective of whether the first MD was experienced during the critical period (around postnatal day 28) or in adulthood, OD shifts induced by a second MD were faster, more persistent and specific to repeated deprivation of the same eye. The capacity for plasticity in the mammalian cortex can therefore be conditioned by past experience.

Aging↗

PubMed2005

Altered map of visual space in the superior colliculus of mice lacking early retinal waves.

During the development of the mammalian retinocollicular projection, a coarse retinotopic map is set up by the graded distribution of axon guidance molecules. Subsequent refinement of the initially diffuse projection has been shown to depend on the spatially correlated firing of retinal ganglion cells. In this scheme, the abolition of patterned retinal activity is not expected to influence overall retinotopic organization, but this has not been investigated. We used optical imaging of intrinsic signals to visualize the complete retinotopic map in the superior colliculus (SC) of mice lacking early retinal waves, caused by the deletion of the beta2 subunit of the nicotinic acetylcholine receptor. As expected from previous anatomical studies in the SC of beta2(-/-) mice, regions activated by individual visual stimuli were much larger and had less sharp borders than those in wild-type mice. Importantly, however, we also found systematic distortions of the entire retinotopic map: the map of visual space was expanded anteriorly and compressed posteriorly. Thus, patterned neuronal activity in the early retina has a substantial influence on the coarse retinotopic organization of the SC.

Animals↗

PubMed2003

Within- and across-channel processing in auditory masking: a physiological study in the songbird forebrain.

Synchronous envelope fluctuations in different frequency ranges of an acoustic background enhance the detection of signals in background noise. This effect, termed comodulation masking release (CMR), is attributed to both processing within one frequency channel of the auditory system and comparisons across separate frequency channels. Here we present data on CMR from a study in field L2 of the auditory forebrain of the European starling (Sturnus vulgaris) using two 25-Hz-wide bands of masking noise that provide the opportunity to distinguish between within-channel and across-channel effects. Acoustically evoked responses were recorded from unrestrained birds via radio telemetry. The signal was a 800 msec pure tone presented at the most sensitive frequency of the units in a previously determined frequency-tuning curve (FTC). One band of masking noise was centered on the signal frequency while the flanking band of noise was presented either within the limits of the excitatory FTC (i.e., within the same frequency channel as the on-frequency masker) or in the suppression area of the FTC (i.e., in a separate channel). For flanking bands inside the excitatory FTC, signal detection thresholds based on the rate code were lower in noise maskers with identical envelope fluctuations (comodulated) than in maskers with uncorrelated envelopes resulting in a neural CMR of approximately 4-7 dB. For flanking bands inside the suppression areas, the neural CMR was reduced. Although the average neural CMR was below the behaviorally determined CMR, a subsample of between 11 and 26% of the recording sites resembled the behavioral performance.

Acoustic Stimulation↗