Selective attention in an insect auditory neuron

Previous work (Pollack, 1986) showed that an identified auditory neuron of crickets, the omega neuron, selectively encodes the temporal structure of an ipsilateral sound stimulus when a contralateral stimulus is presented simultaneously, even though the contralateral stimulus is clearly encoded when it is presented alone. The present paper investigates the physiological basis for this selective response. The selectivity for the ipsilateral stimulus is a result of the apparent intensity difference of ipsi- and contralateral stimuli, which is imposed by auditory directionality; when simultaneous presentation of stimuli from the 2 sides is mimicked by presenting low- and high-intensity stimuli simultaneously from the ipsilateral side, the neuron responds selectively to the high-intensity stimulus, even though the low-intensity stimulus is effective when it is presented alone. The selective encoding of the more intense (= ipsilateral) stimulus is due to intensity-dependent inhibition, which is superimposed on the cell's excitatory response to sound. Because of the inhibition, the stimulus with lower intensity (i.e., the contralateral stimulus) is rendered subthreshold, while the stimulus with higher intensity (the ipsilateral stimulus) remains above threshold. Consequently, the temporal structure of the low-intensity stimulus is filtered out of the neuron's spike train. The source of the inhibition is not known. It is not a consequence of activation of the omega neuron. Its characteristics are not consistent with those of known inhibitory inputs to the omega neuron.     

Pharmaco-MEG evidence for attention related hyper-connectivity between auditory and prefrontal cortices in ADHD

The ability to attend to particular stimuli while ignoring others is crucial in goal-directed activities and has been linked with prefrontal cortical regions, including the dorsolateral prefrontal cortex (DLPFC). Both hyper- and hypo-activation in the DLPFC has been reported in patients with attention-deficit/hyperactivity disorder (ADHD) during many different cognitive tasks, but the network-level effects of such aberrant activity remain largely unknown. Using magnetoencephalography (MEG), we examined functional connectivity between regions of the DLPFC and the modality-specific auditory cortices during an auditory attention task in medicated and un-medicated adults with ADHD, and those without ADHD. Participants completed an attention task in two separate sessions (medicated/un-medicated), and each session consisted of two blocks (attend and no-attend). All MEG data were coregistered to structural MRI, corrected for head motion, and projected into source space. Subsequently, we computed the phase coherence (i.e., functional connectivity) between DLPFC regions and the auditory cortices. We found that un-medicated adults with ADHD exhibited greater phase coherence in the beta (14–30 Hz) and gamma frequency (30–56 Hz) range in attend and no-attend conditions compared to controls. Stimulant medication attenuated these differences, but did not fully eliminate them. These results suggest that aberrant bottom-up processing may engulf executive resources in ADHD.     

Selective spatial attention to left or right hand flutter sensation modulates the steady-state somatosensory evoked potential

Steady-state somatosensory evoked potentials (SSSEPs) were recorded from the scalp of human subjects elicited by 20 and 26 Hz mechanical vibrations applied simultaneously to the index finger of the left (20 Hz) and right hand (26 Hz). Subjects were instructed to attend to the flutter vibration at one finger while ignoring the other finger and to detect rare target events at the to-be-attended finger. The amplitude of the frequency coded SSSEP elicited by the attended vibration was significantly enlarged when attention was focused at the respective finger. This amplitude enhancement with attention was most prominent over fronto-central electrode locations contralateral to the attended finger. This is the first report to show the attentional modulation of the SSSEP amplitude in humans, suggesting an enhancement of neural responses in the sense of flutter with attention. The findings will open a new approach for studying the neural mechanisms of sustained selective attention in somatosensation.     

Selective attention and auditory event-related potentials in somatization disorder

Janet suggested a disorder of attention was fundamental to hysteria. This idea was investigated in this study by examining mismatch negativity (MMN), which depends upon a subtraction of cortical potentials evoked by background stimuli from those evoked by target stimuli. Ten patients with somatization disorder (SMD) were compared with ten normal individuals. MMN was smaller in somatizers, particularly at the central recording site. One interpretation of this observation is that somatizers respond more similarly than normals to "relevant" and "irrelevant" stimuli. This finding of an impairment in attentional processing in somatization disorder suggests a subtle neurophysiological disturbance.     

Intersensory selective attention and temporal orienting operate in parallel and are instantiated in spatially distinct sensory and motor cortices

Knowledge about the sensory modality in which a forthcoming event might occur permits anticipatory intersensory attention. Information as to when exactly an event occurs enables temporal orienting. Intersensory and temporal attention mechanisms are often deployed simultaneously, but as yet it is unknown whether these processes operate interactively or in parallel. In this human electroencephalography study, we manipulated intersensory attention and temporal orienting in the same paradigm. A continuous stream of bisensory visuo‐tactile inputs was presented, and a preceding auditory cue indicated to which modality participants should attend (visual or tactile). Temporal orienting was manipulated blockwise by presenting stimuli either at regular or irregular intervals. Using linear beamforming, we examined neural oscillations at virtual channels in sensory and motor cortices. Both attentional processes simultaneously modulated the power of anticipatory delta‐ and beta‐band oscillations, as well as delta‐band phase coherence. Modulations in sensory cortices reflected intersensory attention, indicative of modality‐specific gating mechanisms. Modulations in motor and partly in somatosensory cortex reflected temporal orienting, indicative of a supramodal preparatory mechanism. We found no evidence for interactions between intersensory attention and temporal orienting, suggesting that these two mechanisms act in parallel and largely independent of each other in sensory and motor cortices. Hum Brain Mapp 36:3246–3259, 2015. © 2015 Wiley Periodicals, Inc.     

fMRI activations of SI and SII cortices during tactile stimulation depend on attention

Somatosensory cortical areas are widely studied with new functional imaging techniques, but usually with poor control over the attentional state of subjects. We applied fMRI to determine possible changes in activations of these areas due to modulations of attention. Attention induced large regional changes, mostly enlargements of activated areas, and more of those at SII than at SI. The number of instances where activation was only seen in attend conditions was also larger at SII than at SI. These results show the importance of controlling the attentional state of the subjects in imaging studies, and give evidence of the different roles of SI and SII cortices in the somatosensory system.     

Naming the same entities from visual or from auditory stimulation engages similar regions of left inferotemporal cortices

We have proposed that the left inferotemporal (IT) region contains structures that mediate between conceptual knowledge retrieval and word-form retrieval, and we have hypothesized that these structures are utilized for word retrieval irrespective of the sensory modality through which an entity is apprehended, thus being "modality neutral." We tested this idea in two sensory modalities, visual and auditory, and for two categories of concrete entities, tools and animals. In a PET experiment, 10 normal participants named tools and animals either from pictures or from characteristic sounds (e.g., "scissors" from a picture of a scissors or from the sound of a scissors cutting; "rooster" from a picture of a rooster or from the sound of a rooster crowing). Visual and auditory naming of tools activated the left posterior/lateral IT; visual and auditory naming of animals activated the left anterior/ventral IT. For both tools and animals, the left IT activations were similar in location and magnitude regardless of whether participants were naming entities from pictures or from sounds. The results provide novel evidence to support the notion that left IT structures contain "modality-neutral" systems for mediating between conceptual knowledge and word retrieval.     

Commissural connections between the auditory cortices of the rat

The pattern of commissural connections of the rat auditory cortex (AC) was investigated with injections of wheat germ agglutinated horseradish peroxidase into the AC. Homotopic and heterotopic patches of neurons were retrogradely labeled in the contralateral hemisphere. Each injection labeled neurons at the corresponding contralateral site, i.e. the homotopic site. In addition, retrogradely labeled neurons were found at non-corresponding locations in contralateral AC, i.e. at heterotopic locations. The pattern of heterotopic labeling changed systematically with the injections. Mapping rules were established that led to the parcellation of areas 41 and 36 into 6 fields. Four fields were defined in Krieg's area 41 (primary AC) and two fields in Krieg's area 36 (secondary AC). In area 41 the heterotopic connection is not reciprocal; in area 36, however, heterotopic projections are organized reciprocally. Contrary to the visual cortex, homotopic and heterotopic projection neurons were equally distributed across the cortical laminae. With double-label experiments it could be shown that a considerable number of the neurons in area 41 bifurcate and project to homotopic as well as to heterotopic sites in the contralateral hemisphere. We conclude that in the AC there are several subtypes of neurons projecting to the contralateral hemisphere; it would be of interest whether these anatomical differences are manifested by physiological differences.     

Verbal dichotic listening in right and left-handed adults: laterality effects of directed attention

Dichotic listening performance of consonant vowel stimuli was studied in 51 adult right- and left-handers in three attention conditions: non-directed and directed to either the right or left ear. In the non-directed condition, a significant right-ear advantage was found in both handedness groups with a stronger asymmetry in right-handers. There are at least three explanations for this ear bias. The classic or structural hypothesis suggests that to the right ear projects more strongly to the language dominant left hemisphere. The callosal relay hypothesis is based on the influence of inhibitory connections via the corpus callosum. The attentional hypothesis suggests that each hemisphere primarily directs attention to contralateral space and because the left hemisphere is dominant for language in both groups, and is aroused by speech stimuli, attention is primarily directed to the right ear. Neither hypothesis can explain why greater than 95% of right-handers have left hemisphere language dominance, but only 70-80% have a right ear bias. Our results demonstrate that in the directed attention conditions both groups increased their lateral biases when directed to either the right or left. The classic or structural hypothesis cannot account for these changes, thereby providing support for the attentional hypothesis. In addition, the right-handed subjects exhibited a greater shift of bias than did the left-handed subjects, when directing their attention leftward. This finding suggests that right-handed people are better able to shift their attention than left-handed people.     

Selective attention differentially affects brainstem auditory evoked potentials of electrodermal responders and nonresponders

Brainstem auditory evoked potentials (BAEPs) were recorded in adult male chronic schizophrenics on maintenance neuroleptic therapy, drug-free alcoholics, and normal subjects. Subjects were subdivided into electrodermal responders (Rs) and nonresponders (NRs). Attention was directed toward auditory or visual stimuli. Independent of diagnosis, latencies of BAEP wave V were longer in NRs when visual rather than auditory stimuli were attended to, while there was no task effect for Rs. This finding is interpreted as a sign of excessive selective filtering of auditory stimuli in NRs. In the alcoholic NRs, wave I-V conduction times were longer than those in any other subgroup, possibly indicating retarded neural transmission.     

Human auditory steady-state evoked potentials during selective attention

The human auditory steady-state evoked potentials were examined during several different tasks requiring attention. Both Fourier analysis and signal averaging were used to measure the responses at stimulus rates between 37 and 41/sec. There was no effect of attention on the amplitude and phase of the steady-state evoked potentials when subjects either counted successive increments in stimulus intensity or read a book. In a dichotic listening task, there were clear changes in the late transient evoked potentials with selective attention but no changes in the steady-state responses. Furthermore, the steady-state potentials recorded during reading were not different from those obtained while the subjects were selectively attending to the auditory stimuli in one ear. There is therefore no evidence that the auditory steady-state responses are affected by attention.     

Selective attention to fearful faces during pregnancy

Background

There is some evidence that pregnancy may be associated with cognitive affective changes, including increased ability to encode emotional faces signaling threat and increased anxiety. Nevertheless, findings to date are inconsistent, and there are few data on correlations with endocrine and hormonal measures. The aim of this study was to investigate danger sensitivity, as measured by selective attention to fearful and angry faces during pregnancy, and to correlate findings with distress and anxiety levels, glucocorticoid (cortisol) and gonadal hormones (estrogen, progesterone and testosterone).

Methods

Selective attention to fearful, angry and happy faces was assessed in pregnant women (n = 44) and non-pregnant controls (n = 25) using a modified version of an emotional Stroop task. General distress was assessed using the K-10, and state and trait anxiety using the Spielberger State-Trait Inventory. Levels of cortisol, estrogen, progesterone and testosterone were determined at trimester 2 and 3. Analyses of variance, regression and correlational analyses were used to investigate associations between variables.

Results

Pregnant women showed altered attentional responses to fearful faces, in comparison to controls. When analyzed according to different levels of distress (K-10 > 20 or K-10 ≤ 20), distressed pregnant women had significantly increased selective attention to fearful faces compared to distressed non-pregnant controls. Attention to fear was significantly associated with increased levels of estrogen and progesterone at trimester 2, and decreased levels of cortisol at trimester 3 of pregnancy.

Conclusion

Heightened sensitivity to danger cues during pregnancy is consistent with a perspective that emphasizes the importance of parental precaution and the adaptive significance of responding to potentially hazardous stimuli during this period. Such changes may be particularly apparent in distressed women, and may be mediated by changes in glucocorticoid and gonadal hormone systems during pregnancy.     

Selective attention to lexical tones recruits left dorsal frontoparietal network

Phonological processing activates a posterior superior region of inferior prefrontal cortex, but questions still remain about the relationship between phonology and this particular region. In this fMRI experiment, subjects were asked to match an intrasyllabic unit (Chinese tones) in an experimental condition vs. whole syllables in a control condition. The only difference between conditions is mediated by focus of attention, either to a subpart (i.e. tone) of the syllable or to the whole syllable itself. Phonetic extraction of Chinese tones reveals a dorsal frontoparietal network in the LH that engages selective attention and internal guidance, two mediational components that are not restricted to phonological processing.     

Selective attention and the auditory vertex potential. Effects of signal intensity and masking noise.

A randomized sequence of tone burst was delivered to subjects at short inter-stimulus intervals (mean ISI of 333 msec), with the tones originating from one to three spatially and frequency-specific channels. The subject's task was to count the tones in one of the three channels at a time, ignoring the other two, and press a button after each tenth tone. In different conditions, tones were given at high (60 dB SL) and low (20 dB SL) intensities and with or without a background white noise to mask the tones. The N1 component of the auditory vertex potential was found to be larger in response to attended-channel tones than in relation to unattended tones. This selective enhancement of N1 was minimal for loud tones presented without noise and increased markedly for the lower tone intensity and in noise-added conditions. The selectivity of attention was measured physiologically in this multichannel listening task was thus greater when tones were faint and/or different to detect.     

Laterally directed arm movements and right unilateral neglect after left hemisphere damage.

Signs of unilateral neglect for events occurring in one hemispace most often result from right hemisphere lesions. Right unilateral neglect after left hemisphere damage is much rarer, and has received less attention. The present study explores the relationships between right unilateral neglect and asymmetries in producing laterally directed arm movements in the horizontal plane in left brain-damaged (LBD) patients. Participants produced right- or left-directed arm movements with their left arm in response to centrally located visual stimuli. Results showed that LBD patients with signs of right unilateral neglect were consistently slowed when producing arm movements toward the right (neglected) side, as compared to left-directed movements. Taking into account patients with and without signs of neglect, this directional asymmetry positively correlated with a reaction-time measure of perceptual spatial bias. These findings stand in contrast with previous results obtained with the same experimental paradigm in right brain-damaged patients, in whom a consistent slowing of leftward-directed movements was rare and apparently unrelated to the presence and severity of left neglect. These conflicting results are discussed with respect to the hypothesis that different mechanisms may underlie left and right unilateral neglect.     

Selective attention and the auditory vertex potential. I. Effects of stimulus delivery rate.

In a selective attention task, twelve subjects received random sequences of 800 and 1500 c/sec tone pips in their right and left ears, respectively. They were instructed to attend to one channel (ear) of tones, to ignore the other, and to press a button whenever occasional "targets", tones of a slightly higher pitch, were detected in the attended ear. In separate experimental conditions the randomized interstimulus intervals (ISIs) were "short" (averaging 350 msec), "medium" (960 mes) and "long" (1920 msec). The N1 component of the auditory evoked potential (latency 80--130 msec) was found to be enlarged to all stimuli in an attended channel (both targets and non-targets) but only in the short ISI condition. Thus, a high "information load" appears to be a prerequisite for producing channel-selective enhancement of the N1 wave; this high load condition was also associated with the most accurate target detectability scores (d'). The pattern of attention-related effects on N1 was dissociated from the pattern displayed by the subsequent P3 wave (300--450 msec), substantiating the view that the two waves are related to different modes of selective attention.     

Functional imaging during covert auditory attention in multiple sclerosis

Recent literature suggests that the brain in multiple sclerosis (MS) undergoes reorganization that subserves the performance of visual and motor tasks. We identified sites of cerebral activity in 16 MS patients while performing a covert attention (CA) task, presented in the auditory modality. Positron emission tomography (PET) revealed activation of rostral/dorsal anterior cingulate cortex (ACC) in normal subjects studied previously. Activity in this region was not significant in MS patients, but there was a large region of activity in superior temporal cortex. Decreased activation of frontal attentional networks and greater activity in sensory/perceptual cortical areas (auditory association cortex) suggests a reduction of transmission along white matter tracts connecting these regions. This study demonstrates cingulate hypoactivity and cerebral reorganization during auditory attention in MS.     

Interhemispheric imbalance during visuospatial attention investigated by unilateral and bilateral TMS over human parietal cortices

We used single-pulse transcranial magnetic stimulation (TMS) to study visuospatial attention. TMS was applied over one hemisphere, or simultaneously over both the right and left posterior parietal cortex (PPC), at two different interstimulus intervals (ISI) during a visual detection task. Unilateral TMS over the right and left PPC, respectively, impaired detection of contralateral presented visual stimuli at an ISI of 150 ms. By contrast, simultaneous biparietal TMS induced no significant changes in correct stimulus detection. TMS at an ISI of 250 ms evoked no changes for magnetic stimulation over either the right or the left parietal cortex. These results suggest that both PPC play a crucial role at a relatively early stage in the widely distributed brain network of visuospatial attention. The abolition of behavioral deficits during simultaneous biparietal TMS underlines the common hypothesis that an interhemispheric imbalance might underlie the disorders of neglect and extinction seen following unilateral brain damage.     

Neuronal effects of nicotine during auditory selective attention in schizophrenia

Although nicotine has been shown to improve attention deficits in schizophrenia, the neurobiological mechanisms underlying this effect are poorly understood. We hypothesized that nicotine would modulate attention‐associated neuronal response in schizophrenia patients in the ventral parietal cortex (VPC), hippocampus, and anterior cingulate based on previous findings in control subjects. To test this hypothesis, the present study examined response in these regions in a cohort of nonsmoking patients and healthy control subjects using an auditory selective attention task with environmental noise distractors during placebo and nicotine administration. In agreement with our hypothesis, significant diagnosis (Control vs. Patient) X drug (Placebo vs. Nicotine) interactions were observed in the VPC and hippocampus. The interaction was driven by task‐associated hyperactivity in patients (relative to healthy controls) during placebo administration, and decreased hyperactivity in patients after nicotine administration (relative to placebo). No significant interaction was observed in the anterior cingulate. Task‐associated hyperactivity of the VPC predicted poor task performance in patients during placebo. Poor task performance also predicted symptoms in patients as measured by the Brief Psychiatric Rating Scale. These results are the first to suggest that nicotine may modulate brain activity in a selective attention‐dependent manner in schizophrenia. Hum Brain Mapp 37:410–421, 2016. © 2015 Wiley Periodicals, Inc.