Biomedical subjects

Nachum Ulanovsky

Publications and source records attributed to Nachum Ulanovsky.

6 recordsLinked to original sources

PubMed2007

Hippocampal cellular and network activity in freely moving echolocating bats.

The hippocampus is crucial for episodic and spatial memory. In freely moving rodents, hippocampal pyramidal neurons show spatially selective firing when the animal passes through a neuron's 'place-field', and theta-band oscillation is continuously present during locomotion. Here we report the first hippocampal recordings from echolocating bats, mammals phylogenetically distant from rodents, which showed place cells very similar to those of rodents. High-frequency 'ripple' oscillations were also rodent-like. Theta oscillation, however, differed from rodents in two important ways: (i) theta occurred when bats explored the environment without locomoting, using distal sensing through echolocation, and (ii) theta was not continuous, but occurred in short intermittent bouts. The intermittence of theta suggests that models of hippocampal function that rely on continuous theta may not apply to bats. Our data support the hypothesis that theta oscillation in the mammalian hippocampus is involved in sequence learning and hence, theta power should increase with sensory-input rate-which explains why theta power correlates with running speed in rodents and with echolocation call rate in bats.

Action Potentials↗

PubMed2006

Responses of neurons in primary auditory cortex (A1) to pure tones in the halothane-anesthetized cat.

The responses of primary auditory cortex (A1) neurons to pure tones in anesthetized animals are usually described as having mostly narrow, unimodal frequency tuning and phasic responses. Thus A1 neurons are believed not to carry much information about pure tones beyond sound onset. In awake cats, however, tuning may be wider and responses may have substantially longer duration. Here we analyze frequency-response areas (FRAs) and temporal-response patterns of 1,828 units in A1 of halothane-anesthetized cats. Tuning was generally wide: the total bandwidth at 40 dB above threshold was 4 octaves on average. FRA shapes were highly variable and many were diffuse, not fitting into standard classification schemes. Analyzing the temporal patterns of the largest responses of each unit revealed that only 9% of the units had pure onset responses. About 40% of the units had sustained responses throughout stimulus duration (115 ms) and 13% of the units had significant and informative responses lasting 300 ms and more after stimulus offset. We conclude that under halothane anesthesia, neural responses show many of the characteristics of awake responses. Furthermore, A1 units maintain sensory information in their activity not only throughout sound presentation but also for hundreds of milliseconds after stimulus offset, thus possibly playing a role in sensory memory.

Acoustic Stimulation↗

PubMed2004

Multiple time scales of adaptation in auditory cortex neurons.

Neurons in primary auditory cortex (A1) of cats show strong stimulus-specific adaptation (SSA). In probabilistic settings, in which one stimulus is common and another is rare, responses to common sounds adapt more strongly than responses to rare sounds. This SSA could be a correlate of auditory sensory memory at the level of single A1 neurons. Here we studied adaptation in A1 neurons, using three different probabilistic designs. We showed that SSA has several time scales concurrently, spanning many orders of magnitude, from hundreds of milliseconds to tens of seconds. Similar time scales are known for the auditory memory span of humans, as measured both psychophysically and using evoked potentials. A simple model, with linear dependence on both short-term and long-term stimulus history, provided a good fit to A1 responses. Auditory thalamus neurons did not show SSA, and their responses were poorly fitted by the same model. In addition, SSA increased the proportion of failures in the responses of A1 neurons to the adapting stimulus. Finally, SSA caused a bias in the neuronal responses to unbiased stimuli, enhancing the responses to eccentric stimuli. Therefore, we propose that a major function of SSA in A1 neurons is to encode auditory sensory memory on multiple time scales. This SSA might play a role in stream segregation and in binding of auditory objects over many time scales, a property that is crucial for processing of natural auditory scenes in cats and of speech and music in humans.

Acoustic Stimulation↗

PubMed2004

Dynamics of jamming avoidance in echolocating bats.

Animals using active sensing systems such as echolocation or electrolocation may experience interference from the signals of neighbouring conspecifics, which can be offset by a jamming avoidance response (JAR). Here, we report JAR in one echolocating bat (Tadarida teniotis: Molossidae) but not in another (Taphozous perforatus: Emballonuridae) when both flew and foraged with conspecifics. In T. teniotis, JAR consisted of shifts in the dominant frequencies of echolocation calls, enhancing differences among individuals. Larger spectral overlap of signals elicited stronger JAR. Tadarida teniotis showed two types of JAR: (i) for distant conspecifics: a symmetric JAR, with lower- and higher-frequency bats shifting their frequencies downwards and upwards, respectively, on average by the same amount; and (ii) for closer conspecifics: an asymmetric JAR, with only the upper-frequency bat shifting its frequency upwards. In comparison, 'wave-type' weakly electric fishes also shift frequencies of discharges in a JAR, but unlike T. teniotis, the shifts are either symmetric in some species or asymmetric in others. We hypothesize that symmetric JAR in T. teniotis serves to avoid jamming and improve echolocation, whereas asymmetric JAR may aid communication by helping to identify and locate conspecifics, thus minimizing chances of mid-air collisions.

Animals↗

PubMed2003

Primary auditory cortex of cats: feature detection or something else?

Neurons in sensory cortices are often assumed to be "feature detectors", computing simple and then successively more complex features out of the incoming sensory stream. These features are somehow integrated into percepts. Despite many years of research, a convincing candidate for such a feature in primary auditory cortex has not been found. We argue that feature detection is actually a secondary issue in understanding the role of primary auditory cortex. Instead, the major contribution of primary auditory cortex to auditory perception is in processing previously derived features on a number of different timescales. We hypothesize that, as a result, neurons in primary auditory cortex represent sounds in terms of auditory objects rather than in terms of feature maps. According to this hypothesis, primary auditory cortex has a pivotal role in the auditory system in that it generates the representation of auditory objects to which higher auditory centers assign properties such as spatial location, source identity, and meaning.

Acoustic Stimulation↗

PubMed2003

Processing of low-probability sounds by cortical neurons.

The ability to detect rare auditory events can be critical for survival. We report here that neurons in cat primary auditory cortex (A1) responded more strongly to a rarely presented sound than to the same sound when it was common. For the rare stimuli, we used both frequency and amplitude deviants. Moreover, some A1 neurons showed hyperacuity for frequency deviants--a frequency resolution one order of magnitude better than receptive field widths in A1. In contrast, auditory thalamic neurons were insensitive to the probability of frequency deviants. These phenomena resulted from stimulus-specific adaptation in A1, which may be a single-neuron correlate of an extensively studied cortical potential--mismatch negativity--that is evoked by rare sounds. Our results thus indicate that A1 neurons, in addition to processing the acoustic features of sounds, may also be involved in sensory memory and novelty detection.

Acoustic Stimulation↗