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At least 1,225 records · Page 68Linked to original sources
PubMed1987

Maps of auditory cortex in cats reared after unilateral cochlear ablation in the neonatal period.

The responses of many neurons recorded in the high best-frequency region of primary auditory cortical field, AI, of the normal adult cat depend upon intensity differences of the sounds arriving at the two ears. These binaural interactions are exhibited early in postnatal life, well before structural maturation of the auditory pathways from the ear to the cortex is complete. The aim of the present work was to study certain aspects of the functional development of the auditory cortex in adult cats unilaterally deaf from birth. In adult animals reared with a neonatal cochlear ablation, field AI ipsilateral to the non-operated ear showed a normal tonotopic map, which was derived from single neurons and neuron clusters driven securely by best-frequency tonal stimulation in virtually every electrode penetration. The acoustic thresholds at many recording sites were as low as those obtained in AI contralateral to the non-operated ear. These findings are in marked contrast to those from control experiments on normal adult cats where only about 65% of AI neurons were excited by a sound delivered to the ipsilateral ear and where thresholds to ipsilateral ear stimulation were significantly higher than contralateral thresholds. The spatial distribution of cortical neurons based on acoustic thresholds also appeared to be different in cats unilaterally deaf from birth when compared to control cats. Closely spaced electrode penetrations in AI ipsilateral to the non-operated ear suggested that neurons were separated into low-threshold regions and high-threshold regions. There was no evidence for this type of non-random segregation in control experiments.

Animals↗
PubMed1983

Habituation of distraction to a tone in the absence of neocortex in rats.

Normal rats and rats with in excess of 95% of neocortex surgically removed (decorticated) were trained to push a food tray door on a Fixed Ratio schedule. Once the behaviour was established a 3720 Hz, 70 dB tone was presented 4 times per session and the duration of distraction from the operant baseline was recorded. Both groups of rats habituated to the presence of the tone within a single session and the effects were retained over a 24 h interval. The decorticates, but not the normal animals, showed a partial spontaneous recovery of the habituated response between sessions. It was concluded that neocortex is not required for either short-term or long-term habituation in this situation though long-term habituation is more complete when neocortex is present.

Animals↗
PubMed1990

Acquired word deafness, and the temporal grain of sound representation in the primary auditory cortex.

This paper explores the nature of the processing disorder which underlies the speech discrimination deficit in the syndrome of acquired word deafness following from pathology to the primary auditory cortex. A critical examination of the evidence on this disorder revealed the following. First, the most profound forms of the condition are expressed not only in an isolation of the cerebral linguistic processor from auditory input, but in a failure of even the perceptual elaboration of the relevant sounds. Second, in agreement with earlier studies, we conclude that the perceptual dimension disturbed in word deafness is a temporal one. We argue, however, that it is not a generalized disorder of auditory temporal processing, but one which is largely restricted to the processing of sounds with temporal content in the milliseconds to tens-of-milliseconds time frame. The perceptual elaboration of sounds with temporal content outside that range, in either direction, may survive the disorder. Third, we present neurophysiological evidence that the primary auditory cortex has a special role in the representation of auditory events in that time frame, but not in the representation of auditory events with temporal grains outside that range.

Animals↗
PubMed1995

Mapping of stimulus features and meaning in gerbil auditory cortex with 2-deoxyglucose and c-Fos antibodies.

The basic functional organization of gerbil auditory cortex was previously mapped with unit recording of best frequency and with the fluoro-2-deoxyglucose mapping (FDG) technique. Among at least seven subfields in this cortex the primary auditory cortex (AI) and the anterior auditory field (AAF) showed prominent tonotopic organization with parallel dorsoventral iso-frequency contours (electrophysiology) in correspondence to FDG labelling of frequency band laminae. In an approach to mechanisms of learning aversive tone conditioning paradigms were found to reshape frequency receptive fields of single units in AI and also produced spatial shifts of tone representation in the tonotopic maps of AI and AAF. Both results suggest that spectral features as well as aspects of behavioural meaning of sounds may be represented even in primary auditory cortex. General meaningfulness in terms of occurrence of novel and salient stimuli may be reflected by expression of immediate early genes. Mapping with an antibody against the immediate early gene product c-Fos was performed in order to identify the spatial distribution of neurons in auditory cortex which change metabolism as a result of stimulation with auditory signals in a new environment. Very short e.g. less than 3 min repetitive stimulation with a tone led to frequency-specific columnar expression of c-Fos in AI and to spare non-tonotopic expression in other fields. Longer stimulation or longer aversive conditioning with the same tone led to spreading of expression, i.e. to accessory non-tonotopic labelling in AI and other fields, particularly pronounced in the output layers V and VI. It is assumed that this spreading relates to the formation of output schemes from auditory cortex in terms of implicit behavioural meaning of stimuli.

Animals↗
PubMed1988

Melodic and harmonic discrimination following unilateral cerebral excision.

Seventy-seven subjects who had undergone unilateral temporal, frontal, or frontotemporal lobectomy for the relief of focal epilepsy as well as a group of 20 normal control subjects were tested in two discrimination tasks, requiring the detection of a single-note change in a pattern of three notes played either successively or simultaneously. Patients with right temporal and right frontotemporal excisions demonstrated a significant deficit in melodic discrimination in comparison to the normal control subjects. Further analysis showed that left-temporal lobectomy including excision of Heschl's gyri (the primary auditory receiving area) led to a significant impairment as well, whereas anterior left temporal-lobe damage did not result in a significant deficit. The results suggest that melodic discrimination depends largely but not exclusively on the right temporal lobe, and that the left Heschl's gyri also seem to be necessary to succeed in this task. In the harmonic task, the differences between the groups did not reach significance, although the two tasks were highly correlated.

Adult↗
PubMedDate not supplied

Effects of information processing demands on slow negative shift latencies and N100 amplitude in selective and divided attention.

The influence of information processing demands on auditory event-related potentials (ERPs) in selective and divided attention was examined by varying the stimulation rate and target difficulty in a two-channel discrimination task. Subjects were required to detect targets in either one or both ears (channels) in a series of tones presented randomly to both ears. The amplitude of the N100 component (latency 80-140 msec) of the ERP to all stimuli in an attended channel was greater if attention was focused on that channel that if it was directed to the opposite channel. N100 amplitude was also reduced in divided attention compared to focused attention. In general, these effects were obtained only if the stimulation rate was high and/or targets were difficult to detect. However, these effects of attention modulated an underlying slow negative shift (SNS) rather than N100 directly. The onset and peak latencies of the SNS were strongly dependent on the processing demands of the task. The results show that the temporal relationship of the SNS to the N100 component is the principal factor responsible for variations in the effects of attention on the ERP with changes in information processing demands. The relationship between these ERP components and resource allocation theories of attention is discussed.

Adolescent↗
PubMedDate not supplied

Event-related potentials during selective attention to speech sounds.

Event-related potentials (ERPs) were recorded from subjects while they selectively attended to sequences of stop-consonant syllables or sequences of tone pips of different frequencies. The ERP difference waveforms that distinguished attended from unattended speech sounds were highly similar in morphology and scalp distribution to the difference waveforms elicited by the tone pips. These results suggest that the attention mechanisms brought into play when selecting complex phonetic stimuli for further analysis are similar to those engaged when selecting between tones of different frequencies, in contrast with previous theoretical interpretations. Latency differences observed between the attention-related ERPs to simple and complex stimuli were attributed to differences in the duration of processing that makes these stimulus features available to attention mechanisms.

Adolescent↗
PubMed1987

Sequential effects on P3 in a counting task: a partial replication.

High and low tones were presented in random order, and the high tones had to be counted. It was intended to replicate the sequential effects on P3 reported by Squires et al. (1976, 1977) and to test by means of an ANOVA approach how each one of the preceding four tones contributes to these sequential effects. However, results deviated from those studies: (1) P3s were generally somewhat larger with target tones than with nontargets; (2) Squires et al.'s (1976, 1977) sequential effects were replicated for nontargets, but were more or less reversed for targets. The preceding sequence was found also to exert influence on prestimulus baselines, N1, and EOG. It is suggested that target effects constitute the rule rather than the exception and that sequential effects on P3 may be altered by subtle differences of subjects' sets, similarly to sequential effects on choice reaction times.

Adolescent↗
PubMed1993

Modification of the acoustic startle-reflex eyeblink: a tool for investigating early and late attentional processes.

The present experiment examined the sensitivity of short and long lead interval startle eyeblink modification to attentional processing. Eighteen college student subjects were presented with a series of intermixed high and low pitched tones and instructed to attend to tones of one pitch and to ignore tones of the other pitch. The majority of the attended and ignored tones served as prepulses for an eyeblink-eliciting burst of white noise presented at lead intervals of 60, 120, 240 and 2000 ms following prepulse onset. Results indicate that both attended and ignored prepulses produce significant startle eyeblink modification: significant blink inhibition at the 60, 120 and 240 ms short lead intervals, and blink facilitation at the 2000 ms long lead interval. In addition, compared with the ignored prepulse, the attended prepulse produced significantly greater blink inhibition at the 120 ms lead interval as well as significantly greater blink facilitation at the 2000 ms lead interval. These results suggest that both short and long lead interval startle eyeblink modification measures may be useful tools for future investigations of the early and later stages of attentional processing.

Acoustic Stimulation↗
PubMed1993

Auditory evoked fields covary with perceptual grouping.

Abrupt acoustic events evoke a transient magnetic response (N100m) at the supratemporal plane. Such responses decrease in amplitude as the interval between successive stimuli decreases to about 1 s. However, when pairs of stimuli are separated by still smaller intervals the second stimulus evokes a larger response than the first. This enhancement depends on the duration of the pause between the offset of the first stimulus and onset of the second. The range over which enhancement of N100m is observed agrees quite well with the range over which subjects experience perceptual grouping of the two stimuli with loudness enhancement of the second. Recordings from multi-channel SQUID gradiometers show that the effect involves not only a change in source strength but also a change in source location within supratemporal cortex. The results suggest that inhibition induced by onset of the first stimulus may be disinhibited by its offset. Physiological and psychological implications are discussed.

Attention↗
PubMed1995

The relation between event-related brain potential, heart rate, and blood pressure responses in an S1-S2 paradigm.

Event-related brain potential (ERP), heart rate (HR), and blood pressure (BP) responses were examined during the 6 s foreperiod of a choice-reaction task. Low and high trait-anxious males were required to make same/different judgements based on the similarity of two successively presented visual patterns. The pitch of a warning tone, presented at the beginning of the foreperiod, indicated whether speed or accuracy was to be emphasized on that trial. In different conditions, subjects received either a monetary reward or aversive noise, depending on their performance. Two clusters of parallel variations were observed in the foreperiod: (1) speed/accuracy instructions affected the amplitude of the CNV and, in interaction with anxiety group, the initial decreases in HR and diastolic BP; (2) type of reward, in interaction with speed/accuracy instructions, affected the amplitude of the P300 and PSW, the mid-interval HR acceleration, and subsequent increases in diastolic and systolic BP. A correlational analysis showed a close relationship between changes in HR and BP, whereas no relationship was evident between changes in ERPs and changes in HR and BP.

Adult↗
PubMed1996

Mismatch negativity subcomponents and ethyl alcohol.

Effects of ethanol (0.55 and 0.85 g/kg) on event-related potentials were investigated by presenting 50-ms standard and 25-ms deviant pure tones to 9 social drinkers during a reading task, in a single-blind, placebo-controlled paradigm. Whereas the lower ethanol dose had no impact on ERPs with an 0.8-s inter-stimulus interval (ISI), it attenuated the N1, P2, and mismatch negativity (MMN) amplitudes with a longer ISI of 2.4 s. The higher alcohol dose increased the N1 peak latency with both ISIs. It also suppressed the N1 and MMN amplitudes with the longer ISI. The MMN suppression did not, however, occur at scalp sites below the Sylvian fissure, thus suggesting that ethanol affected only the frontal MMN subgenerator. Moreover, the different dose responses of the N1, P2, and MMN (subcomponents) to ethanol may indicate that the neurotransmitter systems underlying their generation are, to some extent, different.

Adult↗
PubMed1996

Effects of lateralized cues on the processing of lateralized auditory stimuli.

We examined the influence of auditory spatial cues on the processing of subsequently presented lateralized auditory target stimuli. In three experiments, effects of the position of the cue on event-related potentials (ERPs) and reaction times (RTs) to the target, which could occur at the same or at a different position to the cue, were examined. In Experiments I and II, stimulus-pairs were delivered via loudspeakers 13 degrees to the right or left of fixation. The cue was task-irrelevant in the sense that it never required a response, whereas the target was task-relevant. In Experiment I, the cue was not informative about the position of the succeeding target, that is, the target was presented at the same or at a different position to the cue with equal probability. In Experiment II, the cue predicted a target with high validity, occurring at the position opposite to the cue. In both experiments, the ERPs to targets presented at the same position as the preceding cue were negatively modulated compared with the ERPs to targets presented at a different position. This negative difference (Nd) between the ERPs to same and different position stimuli occurring between 200-300 ms relative to target onset was also obtained in situations where no overt behavior was required. Effects of cue position on RTs to the target were only observed in Experiment II, being shorter for validly predicted targets. These Nd effects either reflect refractoriness of location-specific exogeneous ERP components or involuntary attentional selection. In order to decide between these alternatives, a third experiment was performed, in which stimulus-pairs were presented via headphones to the left and right ear in attend and ignore condition. An Nd effect was obtained in the attend condition only. The absence of Nd effects in the ignore condition suggests that the Nd obtained in attend condition cannot completely be explained by refractoriness of exogeneous ERP components and thus reflects attentional processes.

Adult↗
PubMed1985

Projections of the reticular complex of the thalamus onto physiologically characterized regions of the medial geniculate body.

Afferents from the reticular complex of the thalamus (RE) to the subdivisions of the medial geniculate body (MGB) in the cat were studied by retrograde axonal transport of horseradish peroxidase injected in sites where single unit responses to tones had been characterized. All MGB subdivisions studied received afferents from the same region of RE corresponding to its ventral posterior third, characterized by large neurons. No obvious differences were seen in the localization of labelled neurons within RE according to which MGB subdivision was injected, except that pars lateralis afferents seemed to originate from somewhat more limited portions of RE.

Animals↗
PubMed1985

Both [1-14C]glucose and 2-[1-14C]deoxyglucose produce selective iso-frequency labelling in the inferior colliculus of the cat with short stimulation periods.

Both [1-14C]glucose and 2-[1-14C]deoxyglucose (2-DG) revealed selective autoradiographic labelling to tones in the inferior colliculus of the cat with short stimulation periods (5-15 min). With longer periods of stimulation (45 min), the selectivity disappeared with glucose but remained with 2-DG. At all stimulation intervals, 2-DG labelling was always more selective than that obtained with glucose. However, the selectivity seen with glucose was good enough to indicate that isotopes of glucose with short half-lives could still be employed to study human functional activity with the positron emission tomography technique, provided that short stimulation periods were used.

Animals↗