Event-related potentials to elementary auditory input in distractible adolescents

ObjectiveThe aim of our study was to examine the role of brain activity related to orienting in distractibility.MethodsEvent-related potentials (ERPs) were recorded in response to intermittently presented, non-attended trains of identical auditory stimuli in otherwise healthy but easily distractible (n=16) and non-distractible (n=16) 15-to-16 year old adolescents.ResultsIn easily distractible adolescents, the first tone in each train elicited a significantly larger N1 response than in non-distractible adolescents. A later positivity in the P3 latency range, which may be correlated with the posterior part of the orienting-related P3, was also significantly larger in distractible than in non-distractible adolescents.ConclusionsThe findings of this study suggests that the susceptibility to distraction in adolescence is characterized by abnormally strong orienting response as indexed by enhanced N1 component, and that distractible adolescents allocate proportionately more attentional resources to the irrelevant stimuli as indexed by larger parietal P3 amplitude to the first stimulus of each train.SignificanceThe results of this study contribute to elucidation of the functional basis of distractibility.     

Persistent frontal P300 brain potential suggests abnormal processing of auditory information in distractible children

The P300 event-related potential (ERP) was studied at the beginning, in the middle, and at the end of an auditory stimulus discrimination task in 70 normal 9-year-old children. Easily distractible children showed frontally a short-latency P300 response to target stimuli throughout the task, whereas in the non-distractible children the corresponding response was distinctly smaller and also showed a tendency to decrease in size towards the end of the task. The short-latency frontal P300 response reflects activation of the brain's orienting networks, and it normally decreases in size when stimuli lose their 'novelty value' with stimulus repetition. Persistent frontal P300 suggest that distractible children continued to show enhanced orienting to stimuli that should have already been well encoded and/or categorized.     

Reduced mismatch negativity (MMN) suggests deficits in pre-attentive auditory processing in distractible children

Mismatch negativity (MMN) event-related brain potential reflects the brain's automatic auditory change detection mechanism that depends on integrity of the auditory sensory memory. We studied MMN in easily distractible (n = 20) and in non-distractible (n = 20) healthy 9-year-old children. Two MMN phases were revealed in both groups: an earlier MMN peak at approximately 220 ms and a later negative slope approximately 300-500 ms after stimulus presentation. The results suggested a strong frontal lobe contribution in the generation of the later MMN phase, and this response was significantly reduced in amplitude in the distractible children. The present findings suggest that distractible children may have deficits in the frontally mediated aspects of auditory sensory memory.     

What does the P300 brain response measure in children? New insight from stimulus sequence studies

The decrease in the P300 brain response latency with increasing age is often taken to reflect maturation of cognitive processes in children. We found that in abnormally distractible children the auditory P300 latency decreased significantly when the inter-target interval (ITI) increased in a stimulus discrimination task. We speculate that the sensory memory trace of the target stimulus may decay in distractible children during longer ITIs, and consequently the next target stimulus may activate the brain's orienting networks that are known to generate shorter latency brain responses. The relative strength by which the functionally different neural networks underlying the cognitive brain responses are activated may contribute significantly to the latency measures of these responses. The presumption that a short P300 latency equals to fast processing may thus be over-simplistic, especially in children.     

Distractibility in AD/HD predominantly inattentive and combined subtypes: the P3a ERP component, heart rate and performance

The current study aimed to investigate whether children and adolescents diagnosed with Attention Deficit/Hyperactivity Disorder Predominantly Inattentive (AD/HD-in; Child n = 24, Adolescent n = 33) and Combined (AD/HD-com; Child n = 30, Adolescent n = 42) subtypes were more distractible than controls (Child n = 54; Adolescents n = 75), by assessing event-related potential (ERP), performance and peripheral arousal measures. All AD/HD groups displayed smaller amplitudes and/or shorter latencies of the P3a ERP component - thought to reflect involuntary attention switching - following task-deviant novel stimuli (checkerboard patterns) embedded in a Working Memory (WM) task. The P3a results suggested that both AD/HD-in and AD/HD-com subtypes ineffectively evaluate deviant stimuli and are hence more "distractible". These abnormalities were most pronounced over the central areas. AD/HD groups did not display any abnormalities in averaged heart rate over the WM task, a measure of peripheral arousal. They did display abnormalities in performance measures from the task, but these were unrelated to P3a abnormalities. AD/HD groups also displayed a number of deficits on Switching of Attention and Verbal Memory tasks, however, the pattern of abnormality mostly reflected general cognitive deficits rather than resulting from distraction.     

Single-unit activity in the auditory cortex of monkeys selectively attending left vs. right ear stimuli.

Single-unit responses were recorded from the auditory cortex of rhesus monkeys that were performing an auditory selective attention task. Acoustic stimuli were presented randomly to either the left or right ear through headphones. In a given block of trials one ear was selected as the ear to be attended, and was indicated by lighting either a left or right response key. The animal's task was to press the lighted key whenever stimuli were presented to the attended ear, but to make no response to stimuli presented to the other ear. The attended ear was alternated on successive blocks of trials. Fourteen of 77 units showed significantly greater rates of evoked discharges for an attended stimulus than for an identical non-attended stimulus. The increase in stimulus-evoked activity was not accompanied by any increase in spontaneous activity or by any changes in the pattern of a unit's response. Changes in firing rate occurred at latencies as early as 20 msec.     

Attention to language: Novel MEG paradigm for registering involuntary language processing in the brain

Previous research indicates that, under explicit instructions to listen to spoken stimuli or in speech-oriented behavioural tasks, the brain's responses to senseless pseudowords are larger than those to meaningful words; the reverse is true in non-attended conditions. These differential responses could be used as a tool to trace linguistic processes in the brain and their interaction with attention. However, as previous studies relied on explicit instructions to attend or ignore the stimuli, a technique for automatic attention modulation (i.e., not dependent on explicit instruction) would be more advantageous, especially when cooperation with instructions may not be guaranteed (e.g., neurological patients, children etc). Here we present a novel paradigm in which the stimulus context automatically draws attention to speech. In a non-attend passive auditory oddball sequence, rare words and pseudowords were presented among frequent non-speech tones of variable frequency and length. The low percentage of spoken stimuli guarantees an involuntary attention switch to them. The speech stimuli, in turn, could be disambiguated as words or pseudowords only in their end, at the last phoneme, after the attention switch would have already occurred. Our results confirmed that this paradigm can indeed be used to induce automatic shifts of attention to spoken input. At ～250ms after the stimulus onset, a P3a-like neuromagnetic deflection was registered to spoken (but not tone) stimuli indicating an involuntary attention shift. Later, after the word-pseudoword divergence point, we found a larger oddball response to pseudowords than words, best explained by neural processes of lexical search facilitated through increased attention. Furthermore, we demonstrate a breakdown of this orderly pattern of neurocognitive processes as a result of sleep deprivation. The new paradigm may thus be an efficient way to assess language comprehension processes and their dynamic interaction with those of attention allocation. It does it in an automatic and task-free fashion, indicating its potential benefit for assessing uncooperative clinical populations.     

Individual differences in mismatch negativity measures of involuntary attention shift.

OBJECTIVE: The purpose of this study was to compare the automatic detection of deviance in introverts and extraverts. Event-related potentials were recorded to standard and deviant stimuli. These were presented either rapidly or slowly. Stimuli that are presented slowly may intrude into consciousness. METHODS: Twenty subjects were tested and divided into introverted and extraverted groups. A 500 Hz standard stimulus was presented on 85% of trials. On the remaining 15% of trials, a 750 Hz deviant was presented. In separate conditions, stimuli were presented rapidly (every 500 ms) or slowly (every 1500 ms). Subjects ignored the stimuli while reading. RESULTS: The deviant stimulus elicited a mismatch negativity (MMN) in both conditions. No inter-group differences in the MMN emerged when a rapid rate of presentation was employed. When a slower rate was employed, a late negativity was significantly larger for the extraverted than the introverted group. This was followed by a late positive wave. CONCLUSION: The late negative-positive complex is thought to reflect intrusiveness. It would therefore appear that extraverts are more distractible than introverts when stimuli are presented slowly.     

Abnormal early stages of task stimulus processing in children with attention-deficit hyperactivity disorder--evidence from event-related gamma oscillations.

OBJECTIVES: Attention-related differences in early stages of stimulus processing were assessed in healthy controls and children with attention-deficit hyperactivity disorder (ADHD) by analyzing phase-locked gamma band (31-63 Hz) responses to auditory stimuli in a selective-attention task. METHODS: A total of 28 children aged 9-12 years (ADHD and matched healthy controls) pressed a button in response to each target stimulus presented at the attended side (right or left). Auditory gamma band responses (GBRs) within 0-120 ms were analyzed at 8 electrodes with wavelet transform. Effects of attended channel, stimulus type, and group were evaluated for GBR power and phase-locking. RESULTS: For both groups, GBRs had a frontal-central distribution, were significantly larger and more strongly phase-locked to target than to non-target stimuli, and did not differentiate the attended from the unattended channel. ADHD children produced larger and more strongly phase-locked GBRs than controls only to right-side stimuli, irrespective of whether these were the attended or the ignored stimuli. CONCLUSIONS: The association between auditory GBR and motor task stimulus in children suggests that phase-locked gamma oscillations may reflect processes of sensory-motor integration. ADHD-related deviations of GBRs indicate that early mechanisms of auditory stimulus processing are altered in ADHD, presumably as a result of impaired motor inhibition.     

Spatial responsiveness of monkey hippocampal neurons to various visual and auditory stimuli.

To investigate involvement of the hippocampal formation in spatial information processing, activity of neurons in the hippocampal formation of the conscious monkey was recorded during presentation of various visual and auditory stimuli from several directions around the monkey. Of 1,047 neurons recorded, 106 (10.1%) responded to some stimuli from one or more directions. Of these 106 neurons with directionally differentiating responsiveness, 49 responded to visual stimulation, 35 to auditory stimulation, and 22 to both. Among 81 neurons, each tested with more than 10 different stimuli, one type responded independent of the nature of the stimulus (nonselective, n = 39), and responses of the other type depended on the nature of the stimulus (selective, n = 42). To investigate effects of change in spatial relations between test stimuli and background stimuli fixed on the monkey or fixed in the environment, 59 of 106 neurons were tested while the experimental apparatus holding the stimulus was moved relative to the monkey. Of these 59 neurons, 36 changed their responsiveness; 7 maintained the magnitude of their responses but changed the response direction with the movement of the apparatus, 5 changed direction regardless of the movement, and 24 did not change direction, but decreased or extinguished responses from the preferred direction. Thirty-two of 106 neurons were also tested by rotating the monkey. The directionally differentiating responsiveness of 11 neurons followed the monkey (egocentric neurons), that of 9 remained in place in the environment (allocentric neurons), and responses of 12 were reversibly extinguished when the monkey was rotated. The results suggest that these hippocampal neurons may be involved in identification of relations among various kinds of stimuli in different spatial frameworks (egocentric or allocentric) and this identification may be developed from multiple sensory modalities.     

Relation of a negative ERP component to response inhibition in a Go/No-go task.

Previous studies have suggested that a negative component (N2) of the event-related potential (ERP), whose peak latency is 200-300 msec after stimulus onset, may vary in amplitude depending on the neuronal activity required for response inhibition. To confirm this, ERPs were recorded in a Go/No-go paradigm in which subjects of one group (HI, n = 10) were asked to respond to Go stimuli with key pressing within a shorter period (less than 300 msec) than those of the other group (LI, n = 10) whose upper limit of the reaction time was relatively longer (less than 500 msec). All subjects had to withhold the Go response to the No-go stimuli without making overt muscle activities. The N2 component was recorded superposed on the initial descending limb of the P300 and other slow deflections, which were attenuated with a digital filter to measure the amplitude of N2. The N2 amplitude was significantly larger to the No-go stimulus than to the Go stimulus in both groups, but the N2 to the No-go stimulus was significantly larger in the HI group than in the LI group. These differences in N2 amplitude between conditions or groups were thought to be independent of other ERP components such as P300 and CNV. These results suggest that at least to some extent N2, which increased in amplitude when a greater effort was required to withhold the Go response, reflects the activity of a response inhibition system of the brain.     

Abnormalities of prepulse inhibition do not depend on blink reflex excitability: a study in Parkinson's disease and Huntington's disease.

OBJECTIVE: Prepulse inhibition of the blink reflex is a robust phenomenon with an interesting physiology and a large potential for clinical applicability. In the study presented here we investigated whether the blink reflex inhibition by a prepulse (BRIP) is influenced by the blink reflex excitability recovery (BRER). METHODS: The study was undertaken in 20 patients with Parkinson's disease (PD), 20 patients with Huntington's disease (HD) and 20 healthy volunteers. BRER was determined by measuring the size of the response to a test supraorbital nerve stimulus as a percentage of the response to a conditioning stimulus at inter-stimuli intervals of 100-1000 ms. BRIP was determined as the percentage reduction induced in the response to a supraorbital nerve stimulus by either a low intensity auditory click or a weak third finger somatosensory stimulus, applied with a leading interval of 50-110 ms. RESULTS: There was a negative correlation between the percentage BRER and the percentage BRIP (Pearson's correlation coefficient of -0.37). BRER was enhanced in 14 PD patients (70%) and 6 HD patients (30%), while it was depressed in 10 HD patients (50%). BRIP was significantly reduced in 15 PD patients (75%) and 16 HD patients (80%). No significant correlation was found between abnormally enhanced BRER and abnormally reduced BRIP in all patients as a group (chi(2)=2.4;P=0.11). A weak correlation was found in PD patients (P=0.019) and no correlation was observed in HD patients (P=0.8). CONCLUSIONS: Our results indicate that an abnormally reduced BRIP was not always accompanied by an abnormally enhanced BRER in patients with HD. The two tests likely assess specific and distinct brainstem functions, and provide different types of information. While BRIP may be the result of a widespread integrative processing of sensory stimuli, BRER likely reflects the excitability of a chain of brainstem inter-neurons. SIGNIFICANCE: BRER and BRIP provide independent information on the state of functionally separate circuits that converge on trigemino-facial brainstem inter-neurons.     

Mismatch negativity of the color modality during a selective attention task to auditory stimuli in children with mental retardation

Event-related potentials (ERPs) in response to a stimulus change in the visual color modality were recorded in normal subjects and children with mental retardation (MR) under selective attention conditions with auditory stimuli. The paradigm included the presentation of a standard (blue color screen, B) or deviant (red, R, or greenish blue color screen, GB) visual stimulus, and a target or non-target tone burst stimulus. In Experiment 1, negativity of the subtracted waveform in response to visual stimuli with a latency of 250-280 ms was clearly observed in the ERPs of normal adults. These potentials prominently appeared at posterior sites in one condition, for which the deviant was GB, but were frontal site-dominant for the other condition. A P300 response to visual deviance was not observed in the GB-B paradigm and the subtracted negativity for this paradigm seemed to be more evident than that for the R-B paradigm. The subtracted negativities could be detected in the range of 180-400 ms after the stimulus onset in control children for the GB-B paradigm. The grand average waves of subtracted ERPs in normal children showed a similar distribution to that in normal adults. Similar subtracted potentials could be recorded with the same paradigm in children with MR, however, the negativities were different in waveform and spatial distribution than in controls. Therefore, the subtracted negativity of the present visual modality represented the analogue of the auditory mismatch negativity (MMN), and so-called 'visual MMN' was detectable in children and even in MR patients when the selective attention was directed to other stimuli.     

Effects of maternity on auditory event-related potentials to human sound

Auditory event-related brain potentials (ERPs) were recorded in response to an emotional (a baby's cry) and a neutral (a word) stimulus in a group of mothers 2-5 days after childbirth (n = 20) and in control women (n = 18) who were not in the state of early motherhood. For each mother, her own infant's cry was recorded and used as the cry stimulus, whereas a strange baby's cry was used for control women. The word stimulus was identical for both groups. Stimuli were presented in intermittent trains in order to study the arousal responses to the first stimuli of the trains, and refractoriness of ERPs during stimulus repetition. The N100 responses were significantly larger in amplitude in mothers than in control women, not only to the emotional cry stimuli but also to the neutral word stimuli. The finding suggests a general increase in alertness and arousal in mothers, which may be necessary in enabling the mother to be continuously alert to her infant's needs. This allows good care of the infant and may be essential in building an emotional tie between the mother and her child.     

Neurophysiological study of facial chorea in patients with Huntington's disease.

OBJECTIVE: Choreic movements of patients with Huntington's disease (HD) may result from an abnormal control of sensory inputs. In order to further examine the pathophysiology of facial choreic movements (FCM), we carried out a neurophysiological study, including prepulse inhibition of the blink reflex (BR), in HD patients with and without FCM. METHODS: The study was conducted in 20 genetically proven HD patients with Unified Huntington Disease Rating Scale (UHDRS) scores of FCM ranging between 0 and 3, and in 12 age-matched healthy volunteers who served as control subjects. We counted the number of spontaneous blinks, recorded the electromyographic activity underlying FCM, and analyzed latency, amplitude, and duration of the BR responses to electrical and auditory stimuli. Prepulse inhibition was studied by comparing the responses to test trials with those to control trials. In control trials BRs were obtained to either a single supraorbital nerve electrical stimulus (EBR) or to a 90dB auditory stimulus (ABR). In test trials, the same stimuli were preceded by the prepulse, which was either a weak acoustic tone or a weak electrical stimulus to the third finger, delivered 30-150 ms before. RESULTS: Spontaneous blinking rate was abnormally low in 3 patients, and abnormally high in 9 patients. Mean duration of the BR was longer in patients than in control subjects. In prepulse trials, the percentage inhibition of the BR was abnormally reduced in 15 patients to at least one sensory modality, and significantly correlated with the score of FCM. CONCLUSIONS: Our results suggest that the severity of FCM in patients with HD might be an expression of a disturbance in motor control partly related to an abnormal processing of sensory inputs. Such abnormality involves circuits used in prepulse inhibition of the BR.     

A study of the sensory requirements for eliciting the pseudopregnancy response

Stimulations of the vagina and cervix were performed with a stimulator designed to grade intravaginal penetration of a rod. Single cervicoginal stimulations performed in estrus or in diestrus II elicited immediate or delayed luteal responses, respectively. The probabilities of both types of response increased as a function of the strength (penetration) and duration of the stimulus. Immediate responses were significantly more probable than delayed responses. The other observed parameters of the response (plasma progesterone and diestrus length) were not related to stimulus magnitude.

The probabilities of immediate or delayed responses were related to rod penetration by power functions, implying an exponential transformation of the received stimulus. An exponential transformation of rod penetration into pressure on the cervix, which occurs at the vaginal level, seems not to contribute substantially to the final exponential transformation.

The relationship between stimulus duration and response probability could not be defined mathematically. No further increase in probability of response was caused by prolonging a deep penetration (24 mm) beyond 5 s (immediated responses) and 15 s (delayed responses).

The novel stimuli from an unusual procedure to immobilize the rat may interfere with the response to cervicovaginal stimulation. However, the extravaginal stimuli the female receives during coitus did not seem to facilitate or inhibit the response to a deep (24 mm) penetration of the rod. The results establish some quantitative relationships between stimulus and response parameters and indicate the impotance of cervicovaginal stimuli, among the multiple sensory stimulations of mating, to induce the luteal response.     

Directed attention and perceptual asymmetry to monaurally presented tones

Forty-eight right-handed Ss were tested for simple reaction time (RT) to a monaurally presented 1000 Hz tone of 250 msec duration. Each S was tested in 3 series comprising 7, 11 and 15 stimulus presentations (trials). In each series all stimuli but one (probe) were presented to a single ear. Ss were divided equally into right or left-ear attention groups on the basis of the ear receiving the non-probe trials. Right-ear attention resulted in equally good RTs to either attended or non-attended ear. Left-ear attention resulted in slower RTs than right-ear attention and showed a significant discrepancy between ears in favor of the non-attended ear. The results are interpreted as showing that neither simulus competition nor language processing are necessary conditions for eliciting auditory asymmetry. The data indicate that a cortically-mediated process of selective attention operates in the production of auditory asymmetries for some non-language sounds and that, as with language perception, it is the left cerebral hemisphere that is primarily involved.     

Reaction time, attention, and impulsivity in epilepsy.

Reaction time, attention, and impulsivity were studied in 112 children with epilepsy (4.5-13 years) using a computerized test. We measured simple reaction time (response with each hand separately to a single stimulus), forced choice reaction time (two stimuli presented in random order, one designated for each hand), and choice reaction time with distraction (two response stimuli, one for each hand, with two additional distracting stimuli randomly inserted). We also measured variability of speed of response and errors of omission and commission. Controls were unaffected children of similar age, ethnic, and socioeconomic backgrounds. Children with epilepsy were significantly slower, more variable, and made more omission errors than control children, even when analysis was limited to epileptic patients with IQ greater than 90, but they did not make more commission (i.e., impulsive) errors. Reaction times were related to IQ, but in general were not related to seizure severity, duration of seizure disorder, or duration of medication use. Untreated patients (N = 13) did not differ from those with antiepileptic drug levels in the therapeutic range on the day of testing (N = 52), but differed significantly from normal patients. Epileptic patients demonstrated significant slowing of reaction time and inattention, but not significant impulsivity, compared to normal children; however, these deficits do not appear to be related specifically to seizure history or treatment.     

Neurophysiological aspects of distractability in schizophrenics: A THEORETICAL ANALYSIS

The aim of the present study was to discuss distractability in schizophrenics in neurophysiological terms. A review of the literature strongly suggested that schizophrenics may be abnormally distractible; that is, show an increased tendency to react to irrelevant stimuli. The neuroanatomical structures most clearly implicated in signs of distractability by neurophysiological and behavioural evidence are the prefrontal (orbital) cortex, the nonspecific thalamocortical projection system, and inhibitory regions of the reticular formation. The disturbed functioning of these structures, it is suggested, could come about as a result of a lowered task-related activation, primarily of the prefrontal cortices. Apparently, dopaminergic activity could influence the regions involved, suggesting adopaminergic component in distractability in schizophrenics. The regions in question may also be influenced by other biochemical systems, such as the serotonergic and noradrenergic systems.     

Habituation of the auditory startle response in cervical dystonia and Parkinson's disease

The auditory startle response (ASR) is a brainstem reflex elicited by an unexpected acoustic stimulus. In focal dystonia (FD), the excitability of brainstem neurons is abnormally enhanced. To identify a possible impact of this pathology on the processing of acoustic stimuli, we studied the habituation of the ASR in patients (n = 11) with FD and compared the findings to those of patients with Parkinson's disease (PD; n = 11) and controls (n = 11). Latencies in FD patients did not differ from those of controls but were delayed in PD patients compared to controls (p < 0.0001). Habituation was normal at the orbicularis oculi muscles but reduced at the sternocleidomastoid muscles in FD (p = 0.005). Habituation in PD was comparable to controls. Normal latencies and sequence activation indicate intact neural pathways mediating the ASR in FD. Impaired habituation of the ASR points towards a reduced inhibition of acoustic stimuli in FD.