Towards a common neural substrate in the immediate and effective inhibition of stuttering

Stuttering can be effectively inhibited via exogenous sensory signals (e.g., speaking in unison or using altered auditory feedback) or by using endogenous motoric strategies (e.g., singing or therapeutically implementing long vowel prolongations to reduce speech rates). We propose that these channels, which superficially appear to be diametrically opposite, centrally converge in the engagement of mirror neurons for fluent gestural productions. Sensory changes incurred via exogenous speech signals allow for direct engagement of mirror systems, while endogenous motor strategies appear to require significant departures from normal speech production (e.g., highly unnatural or droned speech) to engage mirror systems. Thus, paradoxically, stuttering is prone to resurface during attempts to impose naturalness upon therapeutic speech.     

The inhibition of stuttering via the perceptions and production of syllable repetitions

In contrast to most therapeutic protocols for stuttering that induce fluency while producing speech targets, we investigated the possibility of inducing "carry-over" fluency prior to normal speech production. Ten adults who stutter read 7-12 syllable phrases after actively producing (via shadowing) or passively listening to: (a) repeating syllables, matched to the initial syllable of the target utterance; (b) repeating syllables, not matched to the initial syllable of the target; (c) nonrepeating syllables; and (d) fricative /noise-like acoustic signals. Relative to baseline, all active syllabic conditions produced approximately 70% inhibition (reduction) of stuttering in the ensuing target utterances, which is attributed to carry-over from fluent shadowing. The most robust passive inhibition (56%) resulted from listening to matched repeating syllables. These findings further sustain that a perception-production link in speech, possibly resulting from mirror neuron activity, can facilitate the inhibition of stuttering. However, in this study we further demonstrate gestural and temporal flexibility of this mechanism, showing that this inhibitory strategy may be enacted prior to producing speech targets. We discuss possible clinical implications and draw comparisons between core stuttering behaviors (i.e., repetitions and prolongations) and behavioral therapeutic strategies (e.g., slowed speech, preparatory sets) used to inhibit or eliminate stuttering.     

Mu wave suppression during the perception of meaningless syllables: EEG evidence of motor recruitment

Motor involvement in speech perception has been recently studied using a variety of techniques. In the current study, EEG measurements from Cz, C3 and C4 electrodes were used to examine the relative power of the mu rhythm (i.e., 8–13 Hz) in response to various audio-visual speech and non-speech stimuli, as suppression of these rhythms is considered an index of ‘mirror neuron’ (i.e., motor) activity. Fourteen adult native English speaking females watched and listened to nine audio-video stimuli clips assembled from three different auditory stimuli (speech, noise, and pure tone) combined with three different video stimuli (speech, noise, and kaleidoscope—made from scrambling an image from the visual speech). Relative to the noise–noise (baseline condition), all visual speech conditions resulted in significant levels of suppression, a finding that is consistent with previous reports of mirror activity to visual speech and mu suppression to ‘biological’ stimuli. None of the non-speech conditions or conditions in which speech was presented via audition only resulted in any significant suppression of the mu rhythm in this population. Thus, visual speech perception appears to be more closely associated with motor activity than acoustic speech perception. It is postulated that in this study, the processing demands incurred by the task were insufficient for inducing significant mu suppression via acoustic speech only. The findings are discussed in theoretical contexts of speech perception and the mirror system. We suggest that this technique may offer a cost-efficient, non-invasive technique for measuring motor activity during speech perception.     

Differential Effects of Endogenous and Exogenous Attention on Sensory Tuning

Covert spatial attention (without concurrent eye movements) improves performance in many visual tasks (e.g., orientation discrimination and visual search). However, both covert attention systems—endogenous (voluntary) and exogenous (involuntary)—exhibit differential effects on performance in tasks mediated by spatial and temporal resolution suggesting an underlying mechanistic difference. We investigated whether these differences manifest in sensory tuning by assessing whether and how endogenous and exogenous attention differentially alter the representation of two basic visual dimensions—orientation and spatial frequency (SF). The same human observers detected a grating embedded in noise in two separate experiments (with endogenous or exogenous attention cues). Reverse correlation was used to infer the underlying neural representation from behavioral responses, and we linked our results to established neural computations via a normalization model of attention. Both endogenous and exogenous attention similarly improved performance at the attended location by enhancing the gain of all orientations without changing tuning width. In the SF dimension, endogenous attention enhanced the gain of SFs above and below the target SF, whereas exogenous attention only enhanced those above. Additionally, exogenous attention shifted peak sensitivity to SFs above the target SF, whereas endogenous attention did not. Both covert attention systems modulated sensory tuning via the same computation (gain changes). However, there were differences in the strength of the gain. Compared with endogenous attention, exogenous attention had a stronger orientation gain enhancement but a weaker overall SF gain enhancement. These differences in sensory tuning may underlie differential effects of endogenous and exogenous attention on performance.SIGNIFICANCE STATEMENT Covert spatial attention is a fundamental aspect of cognition and perception that allows us to selectively process and prioritize incoming visual information at a given location. There are two types: endogenous (voluntary) and exogenous (involuntary). Both typically improve visual perception, but there are instances where endogenous improves perception but exogenous hinders perception. Whether and how such differences extend to sensory representations is unknown. Here we show that both endogenous and exogenous attention mediate perception via the same neural computation—gain changes—but the strength of the orientation gain and the range of enhanced spatial frequencies depends on the type of attention being deployed. These findings reveal that both attention systems differentially reshape the tuning of features coded in striate cortex.     

Progressive Supranuclear Palsy in a family with TDP-43 pathology

The discovery of mirror neurons in macaque has led to a resurrection of motor theories of speech perception. Although the majority of lesion and functional imaging studies have associated perception with the temporal lobes, it has also been proposed that the ‘human mirror system’, which prominently includes Broca's area, is the neurophysiological substrate of speech perception. Although numerous studies have demonstrated a tight link between sensory and motor speech processes, few have directly assessed the critical prediction of mirror neuron theories of speech perception, namely that damage to the human mirror system should cause severe deficits in speech perception. The present study measured speech perception abilities of patients with lesions involving motor regions in the left posterior frontal lobe and/or inferior parietal lobule (i.e., the proposed human ‘mirror system’). Performance was at or near ceiling in patients with fronto-parietal lesions. It is only when the lesion encroaches on auditory regions in the temporal lobe that perceptual deficits are evident. This suggests that ‘mirror system’ damage does not disrupt speech perception, but rather that auditory systems are the primary substrate for speech perception.     

Are mirror neurons the basis of speech perception? Evidence from five cases with damage to the purported human mirror system

The discovery of mirror neurons in macaque has led to a resurrection of motor theories of speech perception. Although the majority of lesion and functional imaging studies have associated perception with the temporal lobes, it has also been proposed that the 'human mirror system', which prominently includes Broca's area, is the neurophysiological substrate of speech perception. Although numerous studies have demonstrated a tight link between sensory and motor speech processes, few have directly assessed the critical prediction of mirror neuron theories of speech perception, namely that damage to the human mirror system should cause severe deficits in speech perception. The present study measured speech perception abilities of patients with lesions involving motor regions in the left posterior frontal lobe and/or inferior parietal lobule (i.e., the proposed human 'mirror system'). Performance was at or near ceiling in patients with fronto-parietal lesions. It is only when the lesion encroaches on auditory regions in the temporal lobe that perceptual deficits are evident. This suggests that 'mirror system' damage does not disrupt speech perception, but rather that auditory systems are the primary substrate for speech perception.     

The temporal order judgment paradigm: subcortical attentional contribution under exogenous and endogenous cueing conditions.

The role of subcortical attentional processing was investigated under exogenous and endogenous cueing conditions. As retinotectal projections arise predominantly from the nasal retina i.e., temporal hemifield, subcortical attention should be distributed asymmetrically under monocular viewing conditions with a temporal hemifield advantage. We compared the results of monocular and binocular viewing conditions using a temporal order judgment (TOJ) paradigm. Subjects fixated a centrally located cross and two stimuli were presented with a variable onset asynchrony. Three experiments were conducted: no cue, exogenous cue and endogenous cue. Subjects reported which stimulus seemed to appear first. An effect consistent with subcortical processing was found under exogenous cueing conditions. No such effect was found under endogenous cueing conditions. We believe that subcortical attentional processing in response to an exogenous cue facilitates rapid shifts in attention towards environmental stimuli. We found no evidence for subcortical processing in voluntary directed attention and believe this process to be cortical in nature.     

Monkey vocalizations and human speech: parallels in perception?

Primate vocal repertoires may be classified along a continuum of discrete vs. graded signals, with the placement of a particular repertoire a result of the interplay between the species' social organization and adaptive specializations of individual signals engendered by the physical environment and their use. Discussion of the different types of graded signals reveals that they may possess either transitional, ontogenetic, or internal variability. Upon examination, the speech of humans is found to contain primarily internally graded signals, and it is suggested that the major phenomena of human speech perception are related to this internally graded quality. Based on this analysis of human speech, it is proposed that other species possessing internal gradings (e.g., Japanese macaques) are also likely to demonstrate similar perceptual phenomena for their own graded vocalizations.     

Attentional modulation and domain‐specificity underlying the neural organization of auditory categorical perception

Categorical perception (CP) is highly evident in audition when listeners’ perception of speech sounds abruptly shifts identity despite equidistant changes in stimulus acoustics. While CP is an inherent property of speech perception, how (if) it is expressed in other auditory modalities (e.g., music) is less clear. Moreover, prior neuroimaging studies have been equivocal on whether attentional engagement is necessary for the brain to categorically organize sound. To address these questions, we recorded neuroelectric brain responses [event‐related potentials (ERPs)] from listeners as they rapidly categorized sounds along a speech and music continuum (active task) or during passive listening. Behaviorally, listeners’ achieved sharper psychometric functions and faster identification for speech than musical stimuli, which was perceived in a continuous mode. Behavioral results coincided with stronger ERP differentiation between prototypical and ambiguous tokens (i.e., categorical processing) for speech but not for music. Neural correlates of CP were only observed when listeners actively attended to the auditory signal. These findings were corroborated by brain‐behavior associations; changes in neural activity predicted more successful CP (psychometric slopes) for active but not passively evoked ERPs. Our results demonstrate auditory categorization is influenced by attention (active > passive) and is stronger for more familiar/overlearned stimulus domains (speech > music). In contrast to previous studies examining highly trained listeners (i.e., musicians), we infer that (i) CP skills are largely domain‐specific and do not generalize to stimuli for which a listener has no immediate experience and (ii) categorical neural processing requires active engagement with the auditory stimulus.     

Covert orienting to exogenous and endogenous cues in children with spina bifida

Children with spina bifida meningomyelocele and hydrocephalus (SBM) have congenital dysmorphology of the midbrain and thinning of the posterior cortex, brain regions associated with the control of covert orienting. We studied cued covert orienting in 92 children with SBM, and 40 age-matched typically developing controls. Cues were of three types: exogenous (luminance change in a peripheral box either valid or invalid for upcoming target location), endogenous arrow (a central arrow either valid or invalid for upcoming target location), or endogenous word (a central word either valid or invalid for upcoming target location). Compared to controls, children with SBM showed slowed covert orienting to both exogenous and endogenous cues and a higher cost of attentional disengagement (e.g., a greater cue-validity effect) for exogenous although not for endogenous cues. Covert orienting deficits were associated with midbrain dysmorphology in the form of beaking of the tectum, and with right posterior brain volume loss.     

The intersection of stress, drug abuse and development.

Use or abuse of licit and illicit substances is often associated with environmental stress. Current clinical evidence clearly demonstrates neurobehavioral, somatic growth and developmental deficits in children born to drug-using mothers. However, the effects of environmental stress and its interaction with prenatal drug exposure on a child's development is unknown. Studies in pregnant animals under controlled conditions show drug-induced long-term alterations in brain structures and functions of the offspring. These cytoarchitecture alterations in the brain are often associated with perturbations in neurotransmitter systems that are intimately involved in the regulation of the stress responses. Similar abnormalities have been observed in the brains of animals exposed to other adverse exogenous (e.g., environmental stress) and/or endogenous (e.g., glucocorticoids) experiences during early life. The goal of this article is to: (1) provide evidence and a perspective that common neural systems are influenced during development both by perinatal drug exposure and early stress exposure; and (2) identify gaps and encourage new research examining the effects of early stress and perinatal drug exposure, in animal models, that would elucidate how stress- and drug-induced perturbations in neural systems influence later vulnerability to abused drugs in adult offspring.     

Comparisons of intervention components within augmentative and alternative communication systems for individuals with developmental disabilities: A review of the literature

Decisions regarding augmentative and alternative communication (AAC) for individuals with developmental disabilities (e.g. what AAC to use and how to teach a person to use a specific AAC modality) should involve consideration of different intervention component options. In an effort to elucidate such decisions and options, this review synthesized 14 studies, published between 2004 and 2012, comparing different AAC intervention components including different symbol sets, instructional strategies, or speech output within aided AAC systems, and different verbal operants within unaided AAC. Evidence supported the following: (a) different instructional strategies such as building motivation, using errorless learning, or adding video models to picture exchange interventions may improve the acquisition or rate of acquisition of picture exchange mands, (b) limited data supports training mimetic (imitated) or mand signs over tacts and (c) differences in symbol sets and speech output levels appeared to have little effect on AAC-based mand acquisition, but listener-based differences should be considered. These findings have implications for future research and clinical practice.     

An ALE meta‐analysis on the audiovisual integration of speech signals

The brain improves speech processing through the integration of audiovisual (AV) signals. Situations involving AV speech integration may be crudely dichotomized into those where auditory and visual inputs contain (1) equivalent, complementary signals (validating AV speech) or (2) inconsistent, different signals (conflicting AV speech). This simple framework may allow the systematic examination of broad commonalities and differences between AV neural processes engaged by various experimental paradigms frequently used to study AV speech integration. We conducted an activation likelihood estimation metaanalysis of 22 functional imaging studies comprising 33 experiments, 311 subjects, and 347 foci examining “conflicting” versus “validating” AV speech. Experimental paradigms included content congruency, timing synchrony, and perceptual measures, such as the McGurk effect or synchrony judgments, across AV speech stimulus types (sublexical to sentence). Colocalization of conflicting AV speech experiments revealed consistency across at least two contrast types (e.g., synchrony and congruency) in a network of dorsal stream regions in the frontal, parietal, and temporal lobes. There was consistency across all contrast types (synchrony, congruency, and percept) in the bilateral posterior superior/middle temporal cortex. Although fewer studies were available, validating AV speech experiments were localized to other regions, such as ventral stream visual areas in the occipital and inferior temporal cortex. These results suggest that while equivalent, complementary AV speech signals may evoke activity in regions related to the corroboration of sensory input, conflicting AV speech signals recruit widespread dorsal stream areas likely involved in the resolution of conflicting sensory signals. Hum Brain Mapp 35:5587–5605, 2014. © 2014 Wiley Periodicals, Inc .     

Neural basis of action understanding: Evidence from sign language aphasia

Background: The neural basis of action understanding is a hotly debated issue. The mirror neuron account holds that motor simulation in fronto-parietal circuits is critical to action understanding including speech comprehension, while others emphasise the ventral stream in the temporal lobe. Evidence from speech strongly supports the ventral stream account, but on the other hand, evidence from manual gesture comprehension (e.g., in limb apraxia) has led to contradictory findings.

Aims: Here we present a lesion analysis of sign language comprehension. Sign language is an excellent model for studying mirror system function in that it bridges the gap between the visual–manual system in which mirror neurons are best characterised and language systems which have represented a theoretical target of mirror neuron research.

Methods & Procedures: Twenty-one life-long deaf signers with focal cortical lesions performed two tasks: one involving the comprehension of individual signs and the other involving comprehension of signed sentences (commands). Participants’ lesions, as indicated on MRI or CT scans, were mapped onto a template brain to explore the relationship between lesion location and sign comprehension measures.

Outcomes & Results: Single sign comprehension was not significantly affected by left hemisphere damage. Sentence sign comprehension impairments were associated with left temporal–parietal damage. We found that damage to mirror system related regions in the left frontal lobe were not associated with deficits on either of these comprehension tasks.

Conclusions: We conclude that the mirror system is not critically involved in action understanding.     

Predictive Neural Computations Support Spoken Word Recognition: Evidence from MEG and Competitor Priming

Human listeners achieve quick and effortless speech comprehension through computations of conditional probability using Bayes rule. However, the neural implementation of Bayesian perceptual inference remains unclear. Competitive-selection accounts (e.g., TRACE) propose that word recognition is achieved through direct inhibitory connections between units representing candidate words that share segments (e.g., hygiene and hijack share /haidʒ/). Manipulations that increase lexical uncertainty should increase neural responses associated with word recognition when words cannot be uniquely identified. In contrast, predictive-selection accounts (e.g., Predictive-Coding) propose that spoken word recognition involves comparing heard and predicted speech sounds and using prediction error to update lexical representations. Increased lexical uncertainty in words, such as hygiene and hijack, will increase prediction error and hence neural activity only at later time points when different segments are predicted. We collected MEG data from male and female listeners to test these two Bayesian mechanisms and used a competitor priming manipulation to change the prior probability of specific words. Lexical decision responses showed delayed recognition of target words (hygiene) following presentation of a neighboring prime word (hijack) several minutes earlier. However, this effect was not observed with pseudoword primes (higent) or targets (hijure). Crucially, MEG responses in the STG showed greater neural responses for word-primed words after the point at which they were uniquely identified (after /haidʒ/ in hygiene) but not before while similar changes were again absent for pseudowords. These findings are consistent with accounts of spoken word recognition in which neural computations of prediction error play a central role.SIGNIFICANCE STATEMENT Effective speech perception is critical to daily life and involves computations that combine speech signals with prior knowledge of spoken words (i.e., Bayesian perceptual inference). This study specifies the neural mechanisms that support spoken word recognition by testing two distinct implementations of Bayes perceptual inference. Most established theories propose direct competition between lexical units such that inhibition of irrelevant candidates leads to selection of critical words. Our results instead support predictive-selection theories (e.g., Predictive-Coding): by comparing heard and predicted speech sounds, neural computations of prediction error can help listeners continuously update lexical probabilities, allowing for more rapid word identification.     

Reading speech from still and moving faces: the neural substrates of visible speech

Speech is perceived both by ear and by eye. Unlike heard speech, some seen speech gestures can be captured in stilled image sequences. Previous studies have shown that in hearing people, natural time-varying silent seen speech can access the auditory cortex (left superior temporal regions). Using functional magnetic resonance imaging (fMRI), the present study explored the extent to which this circuitry was activated when seen speech was deprived of its time-varying characteristics. In the scanner, hearing participants were instructed to look for a prespecified visible speech target sequence ("voo" or "ahv") among other monosyllables. In one condition, the image sequence comprised a series of stilled key frames showing apical gestures (e.g., separate frames for "v" and "oo" [from the target] or "ee" and "m" [i.e., from nontarget syllables]). In the other condition, natural speech movement of the same overall segment duration was seen. In contrast to a baseline condition in which the letter "V" was superimposed on a resting face, stilled speech face images generated activation in posterior cortical regions associated with the perception of biological movement, despite the lack of apparent movement in the speech image sequence. Activation was also detected in traditional speech-processing regions including the left inferior frontal (Broca's) area, left superior temporal sulcus (STS), and left supramarginal gyrus (the dorsal aspect of Wernicke's area). Stilled speech sequences also generated activation in the ventral premotor cortex and anterior inferior parietal sulcus bilaterally. Moving faces generated significantly greater cortical activation than stilled face sequences, and in similar regions. However, a number of differences between stilled and moving speech were also observed. In the visual cortex, stilled faces generated relatively more activation in primary visual regions (V1/V2), while visual movement areas (V5/MT+) were activated to a greater extent by moving faces. Cortical regions activated more by naturally moving speaking faces included the auditory cortex (Brodmann's Areas 41/42; lateral parts of Heschl's gyrus) and the left STS and inferior frontal gyrus. Seen speech with normal time-varying characteristics appears to have preferential access to "purely" auditory processing regions specialized for language, possibly via acquired dynamic audiovisual integration mechanisms in STS. When seen speech lacks natural time-varying characteristics, access to speech-processing systems in the left temporal lobe may be achieved predominantly via action-based speech representations, realized in the ventral premotor cortex.     

The anti-ghrelin Spiegelmer NOX-B11-3 blocks ghrelin- but not fasting-induced neuronal activation in the hypothalamic arcuate nucleus

The hypothalamic arcuate nucleus (Arc) is the presumed target site for the orexigenic hormone ghrelin, which is secreted from the stomach during fasting. Ghrelin directly activates Arc neurones. Similar to exogenous ghrelin, overnight food deprivation also induces c-Fos expression in the Arc of mice. In the present study, we tested the role of endogenous ghrelin in the fasting-induced c-Fos expression in the Arc of mice. We used NOX-B11-3, the latest generation of the recently developed ghrelin-binding compounds, so-called RNA Spiegelmers (SPM) to block endogenous ghrelin action during food deprivation. The specificity and potency of this compound was also tested in electrophysiological and immunohistological experiments. In electrophysiological in vitro single cell recordings, NOX-B11-3 effectively blocked the excitatory effect of ghrelin in the medial Arc (ArcM) of rats whereas the biologically inactive control SPM had no effect. Furthermore, NOX-B11-3 (15 mg/kg i.p.) potently suppressed ghrelin-induced (25 µg/kg s.c., 12 h after SPM injection) c-Fos expression in the Arc. However, when injected at the beginning of a 14-h fasting period, the same dose of NOX-B11-3 had no effect on the c-Fos expression in the Arc of mice. These results demonstrate that NOX-B11-3 is a long-acting compound, which effectively blocks the effect of exogenous ghrelin on neuronal activity in the Arc under in vitro and in vivo conditions. Furthermore, increased ghrelin signalling does not appear to be a necessary factor for the activation of Arc neurones during food deprivation or other fasting-related signals might have masked or compensated for the loss of the ghrelin effect.     

The frontal cortex and exogenous attentional orienting

Normal functioning of the attentional orienting system is critical for effective behavior and is predicated on a balanced interaction between goal-directed (endogenous) processes and stimulus-driven (exogenous) processes. Although both systems have been subject to much investigation, little is known about the neural underpinnings of exogenous orienting. In the present study, we examined the early facilitatory effects and later inhibition of return effects of exogenous cues in patients with frontal and parietal lesions. Three novel findings emerged from this study. First, unilateral frontoparietal damage appears not to affect the early facilitation effects of exogenous cues. Second, dorsolateral prefrontal damage, especially lesions involving the inferior frontal gyrus, produces an exogenous disengage deficit (i.e., the sluggish withdrawal of attention from the ipsilesional to the contralesional field). Third, a subset of patients with dorsolateral prefrontal damage, with lesions involving the middle frontal gyrus, have a reorienting deficit that extends in duration well beyond established boundaries of the normal reflexive orienting system. These results suggest that the dorsolateral prefrontal cortex plays an important role in exogenous orienting and that component processes of this system may be differentially impaired by damage to different parts of the dorsolateral prefrontal cortex.     

Combined endogenous and exogenous disinhibition of intracortical circuits augments plasticity induction in the human motor cortex

BackgroundMotor imagery (MI) engages cortical areas in the human brain similar to motor practice. Corticospinal excitability (CSE) is facilitated during but not after MI practice. We hypothesized that lasting CSE changes could be achieved by associatively pairing this endogenous modulation with exogenous stimulation of the same intracortical circuits.MethodsWe combined MI with a disinhibition protocol (DIS) targeting intracortical circuits by paired-pulse repetitive transcranial magnetic stimulation in one main and three subsequent experiments. The follow-up experiments were applied to increase effects, e.g., by individualizing inter-stimulus intervals, adding neuromuscular stimulation and expanding the intervention period. CSE was captured during (online) and after (offline) the interventions via input-output changes and cortical maps of motor evoked potentials. A total of 35 healthy subjects (mean age 26.1 ± 2.6 years, 20 females) participated in this study.ResultsA short intervention (48 stimuli within ∼90s) increased CSE. This plasticity developed rapidly, was associative (with MI_on, but not MI_off or REST) and persisted beyond the intervention period. Follow-up experiments revealed the relevance of individualizing inter-stimulus intervals and of consistent inter-burst periods for online and offline effects, respectively. Expanding this combined MI/DIS intervention to 480 stimuli amplified the sustainability of CSE changes. When concurrent neuromuscular electrical stimulation was applied, the plasticity induction was cancelled.ConclusionsThis novel associative stimulation protocol augmented plasticity induction in the human motor cortex within a remarkably short period of time and in the absence of active movements. The combination of endogenous and exogenous disinhibition of intracortical circuits may provide a therapeutic backdoor when active movements are no longer possible, e.g., for hand paralysis after stroke.     

The febrile response to lipopolysaccharide is blocked in cyclooxygenase-2(-/-), but not in cyclooxygenase-1(-/-) mice

Various lines of evidence have implicated inducible cyclooxygenase-2 (COX-2) in fever production. Thus, its expression is selectively enhanced in brain after peripheral exogenous (e.g., lipopolysaccharide [LPS]) or endogenous (e.g., interleukin-1) pyrogen administration, while selective COX-2 inhibitors suppress the fever induced by these pyrogens. In this study, we assessed the febrile response to LPS of congenitally constitutive COX-1 (COX-1-/-) and COX-2 (COX-2-/-)-deficient C57BL/6J-derived mice. COX-1+/- and COX-2+/- mice were also evaluated; controls were wild-type C57BL/6J mice (Jackson Labs.). All the animals were pretrained daily for two weeks to the experimental procedures. LPS was injected intraperitoneally at 1 microgram/mouse; pyrogen-free saline (PFS) was the vehicle and control solution. Core temperatures (Tcs) were recorded using thermocouples inserted 2 cm into the colon. The presence of the COX isoforms was determined in cerebral blood vessels immunocytochemically after the experiments, without knowledge of the functional results. The data showed that the wild-type, COX-1+/-, and COX-1-/- mice all responded to LPS with a 1 degrees C rise in Tc within 1 h; the fever gradually abated over the next 4 h. By contrast, COX-2+/- and COX-2-/- mice displayed no Tc rise after LPS. PFS did not affect the Tc of any animal. It would appear therefore that COX-2 is necessary for LPS-induced fever production.