Biomedical subjects

Timo Ruusuvirta

Publications and source records attributed to Timo Ruusuvirta.

11 recordsLinked to original sources

PubMed2006

Memory-based detection of rare sound feature combinations in anesthetized rats.

It is unclear whether the ability of the brain to discriminate rare from frequently repeated combinations of sound features is limited to the normal sleep/wake cycle. We recorded epidural auditory event-related potentials in urethane-anesthetized rats presented with rare tones ('deviants') interspersed with frequently repeated ones ('standards'). Deviants differed from standards either in frequency alone or in frequency combined with intensity. In both cases, deviants elicited event-related potentials exceeding in amplitude event-related potentials to standards between 76 and 108 ms from the stimulus onset, suggesting the independence of the underlying integrative and memory-based change detection mechanisms of the brain from the normal sleep/wake cycle. The relations of these event-related potentials to mismatch negativity and N1 in humans are addressed.

Acoustic Stimulation↗

PubMed2006

Proactive interference in a two-tone pitch-comparison task without additional interfering tones.

Two-tone pitch-comparison tasks typically comprise several successive pairs of successive tones separated by silent intervals. The serial occurrence of such pairs has been associated with degraded task performance, but the nature of this association is not fully understood. Human adult participants were presented with successive pairs of successive tones. The latter, to-be-compared tone of a pair could differ from the former, to-be-remembered tone of 1046.5 Hz by no more than +/-15 Hz (25 cents). The direction of this difference was easier to identify when it was opposite to that of the preceding pair than when being the same. Merely responding accordingly (irrespectively of whether the response was correct or not) was found not to account for this finding. Our study demonstrates proactive interference in a two-tone pitch comparison task as the difficulty to remember when the first tone of the present pair occurred relative to the last tone of the immediately preceding pair.

Acoustic Stimulation↗

PubMed2006

Cooling of the cerebellar interpositus nucleus abolishes somatosensory cortical learning-related activity in eyeblink conditioned rabbits.

Nictitating membrane movement and multiple-unit activity in the somatosensory cortex were recorded from rabbits during paired (N=6) and unpaired (N=5) presentations of a tone conditioned stimulus (CS) and an airpuff unconditioned stimulus (US). A behavioural conditioned response (CR) to the CS and an accompanying neural response in the somatosensory cortex developed only in the paired group. Inactivation of the cerebellar interpositus nucleus abolished both the acquired CR and the accompanying neural response. However, the CS facilitated both behavioural and neural responses to the US during the inactivation. Thus, the absence of the CR could not be accounted for by the general inability of the CS to alter the behaviour constituting the CR or the activity of the somatosensory cortex. These findings suggest that the efferent copy of the signal related to the eyeblink CR is projected from the cerebellum to the cerebral cortical areas of the US modality.

Animals↗

PubMed2005

A kind of auditory 'primitive intelligence' already present at birth.

'Primitive intelligence' in audition refers to the capacity of the auditory system to adaptatively model the acoustic regularity and react neurophysiologically to violations of such regularity, thus supporting the ability to predict future auditory events. In the present study, event-related brain potentials to pairs of tones were recorded in 11 human newborns to determine the infants' ability to extract an abstract acoustic rule, the direction of a frequency change. Most of the pairs (standard, P = 0.875) were of ascending frequency (i.e. the second tone higher than the first), while the remaining pairs (deviant, P = 0.125) were of descending frequency (the second tone being lower). Their frequencies varied among seven levels to prevent discrimination between standard and deviant pairs on the basis of absolute frequencies. We found that event-related brain potentials to deviant pairs differed in amplitude from those to standard pairs at 50-450 ms from the onset of the second tone of a pair, indicating the infants' ability to represent the abstract rule. This finding suggests the early ontogenetic origin of 'primitive intelligence' in audition that eventually may form a prerequisite for later language acquisition.

Acoustic Stimulation↗

PubMed2004

The human brain processes visual changes that are not cued by attended auditory stimulation.

Event-related potentials (ERPs) to visual stimuli were recorded from the scalp of eight adult humans performing a task in which they counted vowels from a heard story. In the oddball condition, a repeated (standard) light bar of 50 ms in duration was rarely (P = 0.1) replaced by a (deviant) one differing in orientation from the standard. In the control condition, standards were simply omitted from the series and only (alone-) deviants retained. In both conditions, visual stimuli were asynchronous with auditory-task-relevant stimuli. ERPs to deviants significantly differed in amplitude from those to standards in the midline electrodes centrally, parietally and occipitally at 160-200 ms from stimulus onset. Occipitally, such a difference was absent between ERPs to alone-deviants and those to standards. The occipital differential ERPs to deviants, which thus could be found only when standards were present in the series, are discussed in the context of the mismatch negativity (MMN).

Acoustic Stimulation↗

PubMed2004

Longer storage of auditory than of visual information in the rabbit brain: evidence from dorsal hippocampal electrophysiology.

Whereas sensory memory in humans has been found to store auditory information for a longer time than visual information, it is unclear whether this is the case also in other species. We recorded hippocampal event-related potentials (ERPs) in awake rabbits exposed to occasional changes in a repeated 50-ms acoustic (1000 versus 2000 Hz) and visual (vertical versus horizontal orientation) stimulus. Three intervals (500, 1500, or 3000 ms) between stimulus repetitions were applied. Whereas acoustic changes significantly affected ERPs with the repetition intervals of 500 and 1500 ms, visual changes did so only with the repetition interval of 500 ms. Our finding, thus, suggests a similarity in sensory processing abilities between human and non-human mammals.

Acoustic Stimulation↗

PubMed2004

The human brain processes repeated auditory feature conjunctions of low sequential probability.

The human brain is known to preattentively trace repeated sounds as holistic entities. It is not clear, however, whether the same holds true if these sounds are rare among other repeated sounds. Adult humans passively listened to a repeated tone with frequent (standard) and rare (deviant) conjunctions of its three features. Six equiprobable variants per conjunction type were assigned from a space built from these features so that the standard variants (P=0.15 each) were not inseparably traceable by means of their linear alignment in this space. Differential scalp-recorded event-related potentials to deviants indicate that the standard variants were traced as repeated wholes despite their preperceptual distinctiveness and resulting rarity among one another.

Acoustic Stimulation↗

PubMed2004

Newborn human brain identifies repeated auditory feature conjunctions of low sequential probability.

Natural environments are usually composed of multiple sources for sounds. The sounds might physically differ from one another only as feature conjunctions, and several of them might occur repeatedly in the short term. Nevertheless, the detection of rare sounds requires the identification of the repeated ones. Adults have some limited ability to effortlessly identify repeated sounds in such acoustically complex environments, but the developmental onset of this finite ability is unknown. Sleeping newborn infants were presented with a repeated tone carrying six frequent (P = 0.15 each) and six rare (P approximately 0.017 each) conjunctions of its frequency, intensity and duration. Event-related potentials recorded from the infants' scalp were found to shift in amplitude towards positive polarity selectively in response to rare conjunctions. This finding suggests that humans are relatively hard-wired to preattentively identify repeated auditory feature conjunctions even when such conjunctions occur rarely among other similar ones.

Acoustic Stimulation↗

PubMed2003

The newborn human brain binds sound features together.

To process a stimulus as a holistic entity, the human brain must be able to conjoin its different features. Previous evidence suggests that this ability emerges during the first months of life, implying its considerable dependence on postnatal development. We recorded human newborn (1-3 days of age) electrical brain responses to frequently occurring (standard) sounds and to rarely occurring (deviant) sounds in a series. Responses to deviants differed from those to standards despite the fact that only the combination of sound frequency and intensity could be used as a cue for discriminating between these sound types. Our finding suggests that the human brain is ready for auditory feature binding very soon after birth.

Acoustic Stimulation↗

PubMed2003

Activity in the rabbit somatosensory cortex reflects the active procedural memory trace of a classically conditioned eyeblink response.

Behavioral responses and neural responses in the somatosensory cortex were recorded in nine rabbits during the unpaired and paired treatments of classical eyeblink conditioning with a tone conditioned stimulus (CS) and an airpuff unconditioned stimulus. During the unpaired treatment, neither the behavioral nor neural responses to the CS were observed. During the paired treatment, behavioral conditioned response (CR), accompanied by neural activity, was developed. In well-trained animals occasional failures to elicit the CR were accompanied by an absence of neural responses. Nevertheless, the CS modified the behavioral unconditioned response in paired trials, implying that the CR-failures could not reflect the inability of the CS to modulate the pathways triggering the behavior constituting the CR. Thus, a close link between CR elicitation and somatosensory cortical neural response was established. Our finding suggests that this neural activity to a tone CS during classical eyeblink conditioning reflects an efferent copy of the procedural memory trace.

Animals↗

PubMed2002

Reflex facilitation during eyeblink conditioning and subsequent interpositus nucleus inactivation in the rabbit (Oryctolagus cuniculus).

In eyeblink conditioning in the rabbit (Oryctolagus cuniculus), not only is a conditioned response (CR) acquired, but also the original reflex is modified as a function of training. In Experiment 1, by comparing unconditioned responses in unpaired and paired groups, 3 types of reflex facilitation were distinguished. One type was linked to exposure to the unconditioned stimuli (USs) and/or experimental setting. The 2nd type was related to the formation of the memory trace for conditioned eyeblink. The 3rd type was linked to the conditioned stimulus immediately preceding the US in the paired group. In Experiment 2, reversible inactivation of the interpositus nucleus (IPN) abolished the CR and reduced the CR-related reflex facilitation, indicating that the latter depends on the plasticity of the IPN.

Animals↗