Spatio–temporal dynamics of olfactory processing in the human brain: an event-related source imaging study

Although brain structures involved in central nervous olfactory processing in humans have been well identified with functional neuroimaging, little is known about the temporal sequence of their activation. We recorded olfactory event-related potentials (ERP) to H₂S stimuli presented to the left and right nostril in 12 healthy subjects. Topographic and source analysis identified four distinct processing steps between 200 and 1000 ms. Activation started ipsilateral to the stimulated nostril in the mesial and lateral temporal cortex (amygdala, parahippocampal gyrus, superior temporal gyrus, insula). Subsequently, the corresponding structures on the contralateral side became involved, followed by frontal structures at the end of the activation period. Thus, based on EEG-related data, current results suggest that olfactory information in humans is processed first ipsilaterally to the stimulated nostril and then activates the major relays in olfactory information processing in both hemispheres. Most importantly, the currently described techniques allow the investigation of the spatial processing of olfactory information at a high temporal resolution.     

Failure to deactivate in the prefrontal cortex in schizophrenia: dysfunction of the default mode network?

BACKGROUND: Functional imaging studies using working memory tasks have documented both prefrontal cortex (PFC) hypo- and hyperactivation in schizophrenia. However, these studies have often failed to consider the potential role of task-related deactivation. METHOD: Thirty-two patients with chronic schizophrenia and 32 age- and sex-matched normal controls underwent functional magnetic resonance imaging (fMRI) scanning while performing baseline, 1-back and 2-back versions of the n-back task. Linear models were used to obtain maps of activations and deactivations in the groups. RESULTS: The controls showed activation in the expected frontal regions. There were also clusters of deactivation, particularly in the anterior cingulate/ventromedial PFC and the posterior cingulate cortex/precuneus. Compared to the controls, the schizophrenic patients showed reduced activation in the right dorsolateral prefrontal cortex (DLPFC) and other frontal areas. There was also an area in the anterior cingulate/ventromedial PFC where the patients showed apparently greater activation than the controls. This represented a failure of deactivation in the schizophrenic patients. Failure to activate was a function of the patients' impaired performance on the n-back task, whereas the failure to deactivate was less performance dependent. CONCLUSIONS: Patients with schizophrenia show both failure to activate and failure to deactivate during performance of a working memory task. The area of failure of deactivation is in the anterior prefrontal/anterior cingulate cortex and corresponds to one of the two midline components of the 'default mode network' implicated in functions related to maintaining one's sense of self.     

Visual and somatosensory processing in the macaque temporal cortex: the role of ‘expectation’

Summary The somatosensory and visual properties of cells in a polymodal region of temporal cortex were studied in 4 awake behaving macaque monkeys. When stimulated passively and out of sight, cells with tactile responses were found to have very large receptive fields covering most of the body surface and an apparent lack of selectivity for size, shape or texture of the tactile stimulus. These properties are equivalent to those described for the anaesthetized preparation (Bruce et al. 1981). Our study revealed that tactile responses were influenced by the degree to which stimuli could be expected. Tactile stimulation arising from active exploration of novel surfaces produced vigourous neuronal responses but equivalent stimulation of the skin arising when the monkey contacted expected surfaces such as itself or items with which it had become familiar produced no responses. The responses of cells to active or passive tactile stimulation were attenuated when the monkey could see the objects causing the stimulation. For cells responsive to more than one sensory modality, visual and somatosensory responses were associated in a compatible manner. Cells responsive to the onset of touch were selective for the sight of objects moving towards the monkey, whereas cells selective for the offset of touch were responsive to the sight of movements away from the monkey.     

Elevated haemoglobin levels in the motor cortex following 1 Hz transcranial magnetic stimulation: a preliminary study

One hertz transcranial magnetic stimulation (TMS) over the motor cortex has been reported to increase activity in the motor cortex contralateral to stimulation, as evidenced by the elevated motor evoked potential on the corresponding hand muscle. Little research, however, has assessed concomitant changes in the haemoglobin level in the unstimulated motor cortex. An aim of this study was to measure the change of oxy- and deoxy-haemoglobin levels in the left motor cortex after 20 min of 1 Hz TMS over the right motor cortex. Subjects carried out a finger to thumb tapping task sequentially with six blocks of ten cycles (30 s on and 60 s off). One block was performed before TMS and five after TMS. The results show that the level of oxyhaemoglobin in the unstimulated cortex increased after TMS over the contralateral hemisphere and that the increase lasted 40 min after 1 Hz stimulation. Deoxy-haemoglobin was slightly decreased during the first 15 min after stimulation. The results identify long term physiological changes resulting from 1 Hz stimulation and help to inform our understanding of interhemispheric interactions in TMS studies.     

Information processing bottlenecks in macaque posterior parietal cortex: an attentional blink?

When two brief stimuli are presented in rapid succession, our ability to attend and recognize the second stimulus is impaired if our attentional resources are devoted to processing the first. Such inability (termed the “attentional blink” in human studies) arises around 200–500 ms following the onset of the first stimulus. We trained two monkeys on a delayed-match-to-sample task where both the location and orientation of two successively presented grating patches had to be matched. When the delay between the two gratings was varied, monkey’s behavioral performance (d′) was affected in a way that was analogous to the attentional blink in humans. Furthermore, a subset of neurons in the monkey’s lateral intraparietal area, known to be crucial in the control of attention, closely followed the variation in d′, even on occasions when d′ followed an atypical pattern. Our results provide the first behavioral demonstration of an attentional bottleneck in the macaque of a type similar to the human attentional blink as well as a possible single-neuron correlate of the phenomenon.     

Is the posterior cruciate ligament destabilized after the tibial cut in a cruciate retaining total knee replacement?: An anatomical study

Introduction/purposeCruciate retaining total knee replacement has been shown to effectively improve pain and quality of life. Successful outcomes depend on many factors, including the maintenance of a competent posterior cruciate ligament. This study sought to anatomically analyze the percentage of PCL injured during a full transverse, tibial cut, thus altering normal function.Materials and methodsOne hundred and thirty five consecutive knee MRIs taken from 2006 to 2011 were selected from a single surgeon's database for this study. Only subjects with non-arthritic knees were considered for this study; the lack of degenerative joint disease (DJD) was confirmed via a radiological report. The optimal view of the PCL's tibial attachment was observed using the sagittal view of the knee, with a T1 signal. One hundred and twenty two usable images were viewed electronically, and measurements were made using the standardized transverse cut implant guidelines. The percentage of PCL remaining following the cut was categorized into five different groups: 0% (no PCL undermined), 1–49%, 50–74%, 75–99% and 100% (PCL undermined entirely).ResultsOverall only 9.0% (n = 11) would have not endured any damage to the PCL with a transverse tibial saw cut, while 79.6% (n = 98) would have had 50% or more of the PCL undermined. Of the 98 patients with more than 50% resected, 52.1% (n = 51 patients) presented complete destabilization of the PCL. The percentage of PCL destabilized was not significant across age groups (p = 0.280), gender (p = 0.586), or operative side (p = 0.460).ConclusionIndependent of age, gender, and operative side, a majority of PCLs are more than 50% destabilized following the standard transverse tibial cut.Level of evidenceII     

Does synchronization reflect a true interaction in the cardiorespiratory system?

Cardiorespiratory synchronization, studied within the framework of phase synchronization, has recently raised interest as one of the interactions in the cardiorespiratory system. In this work, we present a quantitative approach to the analysis of this nonlinear phenomenon. Our primary aim is to determine whether synchronization between HR and respiration rate is a real phenomenon or a random one. First, we developed an algorithm, which detects epochs of synchronization automatically and objectively. The algorithm was applied to recordings of respiration and HR obtained from 13 normal subjects and 13 heart transplant patients. Surrogate data sets were constructed from the original recordings, specifically lacking the coupling between HR and respiration. The statistical properties of synchronization in the two data sets and in their surrogates were compared. Synchronization was observed in all groups: in normal subjects, in the heart transplant patients and in the surrogates. Interestingly, synchronization was less abundant in normal subjects than in the transplant patients, indicating that the unique physiological condition of the latter promote cardiorespiratory synchronization. The duration of synchronization epochs was significantly shorter in the surrogate data of both data sets, suggesting that at least some of the synchronization epochs are real. In view of those results, cardiorespiratory synchronization, although not a major feature of cardiorespiratory interaction, seems to be a real phenomenon rather than an artifact.     

Visual attention in the rat: a role for the prelimbic cortex and thalamic nuclei?

The behavioral effects of lesions of the prelimbic cortex (PL), mediodorsal nucleus of the thalamus (MD), and anterior thalamic nuclei (ANT) were investigated in 2 attentional tasks in rats: the 5-choice serial reaction time task and a vigilance task. Although there was no lesion effect on accuracy in the 5-choice task, PL lesions enhanced perseverative responding during baseline performance and when stimulus duration was reduced. In contrast, MD lesions increased premature responding during baseline performance and when the intertrial interval was varied unpredictably. In the vigilance paradigm, PL lesions also impaired rats' ability to detect the light signal at baseline and at the reduced stimulus duration. ANT lesions did not substantially disrupt performance. The results suggest that different aspects of attention may be attributable to the PL and the MD and that the mechanisms underlying inhibitory control of behavior may be attributable to functionally different thalamocortical circuits.     

The visual cortex in schizophrenia: alterations of gyrification rather than cortical thickness—a combined cortical shape analysis

In light of bottom-up models of disrupted cognition in schizophrenia, visual processing deficits became a key feature for the pathophysiology of schizophrenia. However, morphometric studies focusing on the visual cortex are limited. Thus, the present study sought to provide a combined cortical shape analysis (cortical thickness, folding) of visual areas, which were implicated to be involved in disturbed visual processing in schizophrenia. A group of 72 patients with schizophrenia according to DSM-IV and 72 age- and gender-matched healthy control subjects were included. All participants underwent high-resolution T1-weighted MRI scans on a 1.5-T scanner. Cortical thickness and mean curvature of the V1, V2 and V5/MT+ visual cortex were estimated using an automated computerized algorithm (Freesurfer Software). A GLM controlling for the effect of age was used to estimate differences of cortical shape parameters between the study groups. Significantly increased gyrification of the V1, V2 and the V5/MT+ visual area bilaterally was detected. Conversely, cortical thickness was reduced in patients with schizophrenia only for the V5/MT+ area. This study is the first providing direct in vivo evidence for a disturbed cortical shape of central visual areas in schizophrenia. The present findings of hypergyria are highly indicative for a disrupted corticogenesis of these visual key regions and might constitute a relevant anatomical basis for visual processing deficits in schizophrenia.     

”Rodent-like” and ”primate-like” types of astroglial architecture in the adult cerebral cortex of mammals: a comparative study

Previous observations disclosed that astroglia with interlaminar processes were present in the cerebral cortex of adult New and Old World monkeys, but not in the rat, and scarcely in the prosimian Microcebus murinus. The present report is a more systematic and comprehensive comparative analysis of the occurrence of such processes in the cerebral cortex of several mammalian species. Brain samples were obtained from adult individuals from the following orders: Carnivora (canine), Rodentia (rat and mouse), Marsupialia (Macropus eugenii), Artiodactyl (bovine and ovine), Scandentia (Tupaia glis), Chiroptera (Cynopteris horsfieldii and C. brachyotis), and Primate: Prosimian (Eulemur fulvus), non-human primate species (Cebus apella, Saimiri boliviensis, Callithrix, Macaca mulatta, Papio hamadryas, Macaca fascicularis, Cercopithecus campbelli and C. ascanius) and from a human autopsy. Tissues were processed for immunocytochemistry using several antibodies directed against glial fibrillary acidic protein (GFAP), with or without additional procedures aimed at the retrieval of antigens and enhancement of their immunocytochemical expression. The cerebral cortex of non-primate species had an almost exclusive layout of stellate astrocytes, with only the occasional presence of long GFAP-IR processes in the dog that barely crossed the extent of lamina I, which in this species had comparatively increased thickness. Species of Insectivora and Chiroptera showed presence of astrocytes with long processes limited to the ventral basal cortex. Interlaminar GFAP-IR processes were absent in Eulemur fulvus, at variance with their limited presence and large within- and inter-individual variability as reported previously in Microcebus murinus. In New World monkeys such processes were absent in Callithrix samples, at variance with Cebus apella and Saimirí boliviensis. Overall, the expression of GFAP-IR interlaminar processes followed a progressive pattern: bulk of non-primate species (lack of interlaminar processes) –Chiroptera and Insectivora (processes restricted to allocortex) <strepsirhini <haplorhini (platirrhini<catarrhini). This trend is suggestive of the emergence of new evolutionary traits in the organization of the cerebral cortex, namely, the emergence of GFAP-IR long, interlaminar processes in the primate brain. Interlaminar processes may participate in a spatially restricted astroglial role, as compared to the one provided by the astroglial syncytium. It is proposed that the widely accepted concept of an exclusively astroglial syncytium is probably linked with a specific laboratory animal species (”rodent-type” or, rather, ”general mammalian-type” model) that misrepresents the astroglial architecture present in the cerebral cortex of most anthropoid adult primates (”primate-type” model), including man. Accepted: 28 June 1999     

Motor activity and imagery modulate the body-selective region in the occipital–temporal area: A near-infrared spectroscopy study

The extrastriate body area (EBA) lies in the occipital–temporal cortex and has been described as a “body-selective” region that responds when viewing other people's bodies. Recently, several studies have reported that EBA is also modulated when the subject moves or imagines moving their own body, even without visual feedback. The present study involved 3 experiments, wherein the first experiment was conducted to examine whether near-infrared spectroscopy (NIRS) could capture any activity in the EBA when viewing images of bodies. The second experiment was designed to elucidate whether this region also responds when the subjects move their own body, and the third to observe whether imagining carrying out a movement would activate EBA. Images of human bodies and chairs were used as the stimuli for the first experiment, simple hand movements carried out by the subject were used for the second and the act of imagining hand movements for the third. Our results confirmed that the region we defined as EBA was clearly activated when the subject viewed images of human bodies, carried out movements of their own body and imagined moving parts of their own body, thus demonstrating the usefulness of NIRS as a new brain imaging method. Moreover, we found a gender-based difference when imagining movement; male subjects showed a greater response than female subjects. This may reflect a gender difference in imagery skills; however, further research is needed to verify this hypothesis.     

The Müller-Lyer illusion seen by the brain: an event-related brain potentials study

Several event-related potential (ERP) studies have demonstrated a negative shift in ERPs for fearful relative to neutral facial expressions 170–300 ms post-stimulus over occipital-temporal scalp. In the present study, three experiments were conducted to examine the importance of the eye region for this ERP differentiation. ERPs and behavioral discrimination responses were measured to fearful and neutral expressions when only the eye region of the expression was visible (the eyes and eyebrows or the eyes alone) and when the eye region (the eyes and eyebrows or the eyes alone) was covered by dark glasses. The results showed a negative shift in ERPs for fearful relative to neutral expressions over lateral temporal sites, starting 160–210 ms post-stimulus. The visibility of the eye region but not the eyes per se was critical for these ERP differences to occur. There were, however, indications that information in the eyes is also coded and used in the categorization of facial expressions.     

Antinociception by motor cortex stimulation in the neuropathic rat: does the locus coeruleus play a role?

We studied whether stimulation of the primary motor cortex (M1) attenuates pain-related spinal withdrawal responses of neuropathic and healthy control rats, and whether the descending antinociceptive effect is relayed through the noradrenergic locus coeruleus (LC). The assessments of the noxious heat-evoked limb withdrawals reflecting spinal nociception and recordings of single LC units were performed in spinal nerve-ligated neuropathic and sham-operated control rats under light pentobarbital anesthesia. Electric stimulation of M1 produced equally strong spinal antinociception in neuropathic and control rats. Following microinjection into M1, a group I metabotropic glutamate receptor agonist (DHPG; 10 nmol) and a high (25 nmol) but not low (2.5 nmol) dose of glutamate slightly increased on-going discharge rates of LC neurons in neuropathic but not in control animals. Influence of electric stimulation of M1 on LC neurons was studied only in the neuropathic group, in which discharge rates of LC neurons were increased by electric M1 stimulation. Lidocaine block of the LC or block of descending noradrenergic influence by intrathecal administration of a α₂-adrenoceptor antagonist failed to produce a significant attenuation of the spinal antinociceptive effect induced by electric M1 stimulation in the neuropathic or the sham group. The results indicate that stimulation of the rat M1 induces spinal antinociception in neuropathic as well as control conditions. While M1 stimulation may activate the LC, particularly in the neuropathic group, the contribution of coeruleospinal noradrenergic pathways may not be critical for the spinal antinociceptive effect induced by M1 stimulation.     

Morphological alterations in the occipital cortex of aged rats with impaired memory: A Golgi–Cox study

This study investigated a possible link between morphological alterations of pyramidal neurons in layer V of the occipital cortex and the degree of spatial memory impairment in aged rats. Measurements of cortical thickness, density of dendritic branching, and spine counts were carried out in young adult (5 months old) and aged (26 months old) Long-Evans female rats on Golgi–Cox silver-stained material. Using the water-maze task, well- and poorly performing rats were distinguished statistically on the basis of their reference-memory scores. When subsequently compared with young rats or to aged rats with good performances, the well-performing rats had a reduced cortical thickness and exhibited weaker high-order branching of basal dendrites on their pyramidal neurons. When dendritic spines were counted on a 50-m-long straight portion of a basal dendrite, no difference was observed between young and aged rats. Our results suggest that structural alterations affecting pyramidal neurons in the occipital cortex of aged rats may contribute to spatial memory impairment. Indeed, in a subpopulation of well-performing aged rats, these structural alterations were less marked than in the population of bad performers.     

The entorhinal cortex of the Megachiroptera: a comparative study of Wahlberg’s epauletted fruit bat and the straw-coloured fruit bat

This study describes the organisation of the entorhinal cortex of the Megachiroptera, straw-coloured fruit bat and Wahlberg’s epauletted fruit bat. Using Nissl and Timm stains, parvalbumin and SMI-32 immunohistochemistry, we identified five fields within the medial (MEA) and lateral (LEA) entorhinal areas. MEA fields E _CL and E _C are characterised by a poor differentiation between layers II and III, a distinct layer IV and broad, stratified layers V and VI. LEA fields E _I, E _R and E _L are distinguished by cell clusters in layer II, a clear differentiation between layers II and III, a wide columnar layer III and a broad sublayer Va. Clustering in LEA layer II was more typical of the straw-coloured fruit bat. Timm-staining was most intense in layers Ib and II across all fields and layer III of field E _R. Parvalbumin-like staining varied along a medio-lateral gradient with highest immunoreactivity in layers II and III of MEA and more lateral fields of LEA. Sparse SMI-32-like immunoreactivity was seen only in Wahlberg’s epauletted fruit bat. Of the neurons in MEA layer II, ovoid stellate cells account for ~38%, polygonal stellate cells for ~8%, pyramidal cells for ~18%, oblique pyramidal cells for ~6% and other neurons of variable morphology for ~29%. Differences between bats and other species in cellular make-up and cytoarchitecture of layer II may relate to their three-dimensional habitat. Cytoarchitecture of layer V in conjunction with high encephalisation and structural changes in the hippocampus suggest similarities in efferent hippocampal → entorhinal → cortical interactions between fruit bats and primates.     

Simple spike firing in the posterior lateral cerebellar cortex of Macaque Mulatta was correlated with success–failure during a visually guided reaching task

Evidence has been accumulating which supports a role for the cerebellum in motor learning. Motor learning is though to be mediated by complex spikes acting as an error signal, which when firing in conjunction with simple spike activity modify synapses between parallel fibers and Purkinje cells. We studied the activity of neurons in the posterior lateral cerebellar cortex of macaques that were performing reaches to visual targets. We found that simple spike firing in many of these neurons was modulated by whether the monkey successfully hit the target or not. The success–failure modulation was present for reaches using either arm and could persist for several hundred milliseconds into a period when the monkey was constrained from moving its arms. This temporally extended success–failure activity could interact with complex spike firing in order to enhance learning, particularly when the motor command is temporally separated from sensory feedback.