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PubMed1995

Emergence of complex receptive field properties of ganglion cells in the developing turtle retina.

1. Receptive field properties of adult retinal ganglion cells are well documented, but little is known about their development. We made extracellular recordings of activity from turtle retinal ganglion cells during embryogenesis (stages 22-26), during the first 40 days posthatching, and in adults. 2. From stage 22 the cells fired in spontaneous recurring bursts, and from stage 23 they responded to light. Polar plots of the responses to motion were highly anisotropic in early embryonic cells. More than 40% of embryonic cells exhibited multiaxis anisotropy, and only 6% were statistically isotropic. The incidence of anisotropic cells gradually decreased throughout development. The incidence of isotropic cells and the excitatory receptive field diameters of all ganglion cells gradually increased during development and their maturation coincided with the disappearance of the spontaneous bursts (2-4 wk posthatching). 3. Both sensitivities to stimulus orientation and direction of motion were observed at the earliest stages of development. However, orientation selectivity reached a peak incidence at hatching, whereas directional selectivity completely disappeared, only to reappear in adults. 4. These results show that mature spatiotemporal receptive field properties of retinal ganglion cells emerge from initially highly anisotropic properties, which may reflect an immature, polarized dendritic layout. Their maturation might be mediated by dendritic outgrowth and strengthening of excitatory synaptic connections, which could be induced by spontaneous activity and driven to maturation by exposure to light at birth. Mature directional selectivity seems to require visual experience or the late establishment of a specialized inhibitory synaptic drive.

Animals↗
PubMed1995

Bipedal reflex coordination to tactile stimulation of the sural nerve during human running.

1. Cutaneous reflex responses were elicited during human running (8 km/h) on a treadmill by electrical stimulation of the sural nerve at the ankle. Stimulus trains (5 pulses of 1 ms at 200 Hz) at three nonnociceptive intensities, which were 1.5, 2.0, and 2.5 times perception threshold (PT), were delivered at 16 phases of the step cycle. For 11 subjects the surface electromyographic (EMG) activity of both the ipsilateral and contralateral long head of the biceps femoris (iBF and cBF, respectively), the semitendinosus (iST and cST), the rectus femoris (iRF and cRF), and the tibialis anterior (iTA and cTA) were recorded. 2. During human running nonnociceptive sural nerve stimulation appears to be sufficient to elicit large, widespread and statistically significant reflex responses, with a latency of approximately 80 ms and a duration of approximately 30 ms. These reflex responses seem to be an elementary property of human locomotion. This is indicated by the occurrence of the responses in all subjects, the consistency of most of the reflex patterns across the subjects and, apart from a small amount of habituation, the reproducibility of the responses during the course of the experiment. 3. The responses are modulated continuously throughout the step cycle such that their magnitude does not in general covary with the background locomotor activities. This is observed most clearly in iST, iTA, and cTA for which statistically significant reflex reversals are demonstrated, and in cRF and cTA for which the responses are gated during most of the step cycle. 4. The response magnitude generally increases as a function of increasing intensity, whereas the phase-dependent reflex modulation is intensity independent. 5. A functional dissociation within the ipsilateral hamstring muscles is demonstrated: the iBF and iST show an antagonistic reflex pattern (facilitatory and suppressive, respectively) during the periods of synergistic background locomotor activity in the step cycle. Contralaterally, however, the cBF and cST are reflexively activated as close synergists during these periods. 6. The reflex responses and their phase-dependent modulation are different for the homologous muscles in the two legs. Yet, some similarities are observed. These are present rather with respect to the phase of the corresponding leg than with respect to the phase of the stimulated leg. Both observations suggest that the phase-dependent reflex modulation is controlled separately in the ipsilateral and contralateral legs. 7. The response simultaneity in all investigated muscles supports the notion of a coordinated cutaneous interlimb reflex during human running.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1998

Temporal and spatial response to second-order stimuli in cat area 18.

Temporal and spatial response to second-order stimuli in cat area 18. J. Neurophysiol. 80: 2811-2823, 1998. Approximately one-half of the neurons in cat area 18 respond to contrast envelope stimuli, consisting of a sinewave carrier whose contrast is modulated by a drifting sinewave envelope of lower spatial frequency. These stimuli should fail to elicit a response from a conventional linear neuron because they are designed to contain no spatial frequency components within the cell's luminance-defined frequency passband. We measured neurons' responses to envelope stimuli by varying both the drift rate and spatial frequency of the contrast modulation. These data were then compared with the same neurons' spatial and temporal properties obtained with luminance-defined sinewave gratings. Most neurons' responses to the envelope stimuli were spatially and temporally bandpass, with bandwidths comparable with those measured with luminance gratings. The temporal responses of these neurons (temporal frequency tuning and latency) were systematically slower when tested with envelope stimuli than with luminance gratings. The simplest kind of model that can accommodate these results is one having separate, parallel streams of bandpass processing for luminance and envelope stimuli.

Algorithms↗
PubMed2000

Spatiotemporal processing of linear acceleration: primary afferent and central vestibular neuron responses.

Spatiotemporal convergence and two-dimensional (2-D) neural tuning have been proposed as a major neural mechanism in the signal processing of linear acceleration. To examine this hypothesis, we studied the firing properties of primary otolith afferents and central otolith neurons that respond exclusively to horizontal linear accelerations of the head (0.16-10 Hz) in alert rhesus monkeys. Unlike primary afferents, the majority of central otolith neurons exhibited 2-D spatial tuning to linear acceleration. As a result, central otolith dynamics vary as a function of movement direction. During movement along the maximum sensitivity direction, the dynamics of all central otolith neurons differed significantly from those observed for the primary afferent population. Specifically at low frequencies (</=0.5 Hz), the firing rate of the majority of central otolith neurons peaked in phase with linear velocity, in contrast to primary afferents that peaked in phase with linear acceleration. At least three different groups of central response dynamics were described according to the properties observed for motion along the maximum sensitivity direction. "High-pass" neurons exhibited increasing gains and phase values as a function of frequency. "Flat" neurons were characterized by relatively flat gains and constant phase lags (approximately 20-55 degrees ). A few neurons ("low-pass") were characterized by decreasing gain and phase as a function of frequency. The response dynamics of central otolith neurons suggest that the approximately 90 degrees phase lags observed at low frequencies are not the result of a neural integration but rather the effect of nonminimum phase behavior, which could arise at least partly through spatiotemporal convergence. Neither afferent nor central otolith neurons discriminated between gravitational and inertial components of linear acceleration. Thus response sensitivity was indistinguishable during 0.5-Hz pitch oscillations and fore-aft movements. The fact that otolith-only central neurons with "high-pass" filter properties exhibit semicircular canal-like dynamics during head tilts might have important consequences for the conclusions of previous studies of sensory convergence and sensorimotor transformations in central vestibular neurons.

Acceleration↗
PubMedDate not supplied

Functional imaging of the auditory system: the use of positron emission tomography.

Modern brain imaging methods now afford unprecedented opportunities for the in vivo study of central auditory system function. Positron emission tomography (PET) has been used as a functional imaging technique for more than 15 years to study the distribution of cerebral haemodynamic changes associated with auditory stimulation, in subjects with normal and abnormal auditory function. Many of these studies concern processes related to, but not identical with, audition, such as speech perception, melodic processing and directed attention. Additionally, PET has been used to explore auditory perception in clinical populations such as cochlear implantees, neurosurgical candidates and people with tinnitus and auditory hallucinations. The spatial resolution of PET does not appear sufficient to address questions of a fine anatomical grain, e.g. exploring functional specialization within the primary and secondary auditory cortex. Nevertheless, PET has considerable potential as a tool in basic research on, and clinical assessment of, many auditory phenomena. Although functional magnetic resonance imaging can now be used for many studies for which formerly only PET was suitable, PET still possesses unique advantages. For example, it permits acquisition of data from inferior frontal and anterior temporal areas, can be used with subjects with cochlear and other implants (such as pacemakers) and can be used to map neurochemical pathways and receptors.

Auditory Cortex↗
PubMed2003

William Feinberg lecture 2002: emotions, mood, and behavior after stroke.

While emotional outcome is a critical factor influencing early evolution and late prognosis after stroke, few relevant studies have been performed on this subject. However, mood changes, modified judgment, and emotional reactions may also dramatically alter recruitment into clinical trials; for instance, up to one third of patients with acute stroke may have altered time perception, inappropriate self-evaluation of their condition, and attentional or memory dysfunction, with a subsequent increase in referral-to-hospital delays. In addition, the value of the "informed" consenting process may be questionable in the setting of urgent randomization into an acute stroke clinical trial. Data from ongoing studies suggest that behavior and emotional reactions in acute stroke patients may be classified into a few broad categories, with considerable overlap. Correlations between mood changes and the type, location, and severity of stroke may provide useful information for improving patient management, including the prediction of functional evolution and late prognosis. While depressive reactions have been widely studied in the recovery-rehabilitation phase after stroke, significant depression is uncommon shortly after stroke. On the other hand, related, though different, emotional behavioral changes may be more frequent; these have often been confused with depression and include catastrophic reaction, emotionalism, and athymhormia. Late depression is the most common mood alteration during the first year after stroke and has specific characteristics that differentiate it from classic endogenous and reactive depression, thus emphasizing the critical role of brain damage in the pathogenesis of poststroke depression. Early recognition and management of mood disorders after stroke are critical for the functional improvement of individual patients. However, little is known about specific indications for different antidepressant drugs in poststroke depression and related disorders. Ongoing research has identified a "new" emotional-behavioral disorder, poststroke fatigue, which is clearly distinct from depression in most instances. It is especially disabling and frustrating in that it typically involves patients with total or near-total neurological recovery, who should have been able to go back to their previous activities but who become severely disabled because of early and persisting exhaustion. Preliminary neuropsychological and MR and PET imaging studies suggest that disruption of subtle mechanisms underlying attention, in the absence of significant cognitive and mood alterations, may be responsible. Research projects are now being launched to better delineate poststroke fatigue and its management.

Acute Disease↗
PubMed1984

The theme of death in complex partial seizures.

The theme of death highlighted the depersonalization phenomena of four patients with complex partial seizures. These patients became preoccupied with death in association with psychomotor seizures, visual hallucinations, and altered perception of time and reality. The episodic sense of being dead or of having an appointment with death is a clue to the diagnosis of recurrent complex partial seizures even without overt motor stigmata of seizures. The syndrome differs from fear of death, steroid psychosis, the "near death syndrome," and Cotard's syndrome. Adjustment of antiseizure medication is an important therapeutic maneuver.

Adult↗
PubMed2002

Spatiotemporal visual processing in schizophrenia.

Studies examining visual processing in schizophrenia have provided inconsistent results. In this study, the authors measured static and dynamic visual contrast sensitivity (CS) in patients with schizophrenia (n=20) and control subjects (n=15). Extrapyramidal symptoms were evaluated with the Simpson-Angus scale. In the static condition, the patients with schizophrenia showed reduced CS in the spatial frequency range of 2.9-14.4 cycles per degree of visual angle (c/d). In the dynamic condition, CS loss was present over the whole range tested (0.5-14.4 c/d). Higher Simpson-Angus scores and higher doses of antipsychotic medication were associated with more severe CS deficits. These results suggest that the hypodopaminergic state induced by antipsychotic medication may produce parkinsonian visual impairments in schizophrenia patients.

Adult↗
PubMedDate not supplied

Temporal resolution of auditory perception and verbal working memory in 15 children with language impairment.

We investigated temporal resolution of auditory perception (TRAP), verbal working memory, and speech perception in 15 children with language impairment (LI) in comparison with a control group of 99 typical children. A computerized two-choice test was used to assess these three abilities. No deficits in TRAP were found in the LI group, and the thresholds were similar for both study groups. It was interesting that the variability was high for both groups and that the control group's performance was poorer than reported in some previously published studies. There were significant differences in the two groups' performance on speech perception and verbal working memory. Working memory was the most sensitive of these two measures.

Auditory Perception↗
PubMed1991

Detection of deficits in temporal pattern discrimination using the seashore rhythm test in young children with reading impairments.

A deficiency in temporal pattern discrimination frequently is a distinguishing characteristic of children with dyslexia or learning disabilities (LD). We studied the feasibility of using the Seashore Rhythm Test, a subtest of the Halstead-Reitan neurological assessment battery (Halstead, 1947), with young children to discriminate children with reading impairments from age-matched controls reading at a normal level, in an effort to develop tools to determine readiness to read in young school-age children. Major considerations in test selection were ease of administration and wide use and acceptance. Fifty-nine children in Grades 1 through 3 were administered a battery of tests during the last 3 weeks of the school year by blinded experimenters. Tests administered included the Seashore Rhythm Test, Benton Visual Retention Test, Peabody Picture Vocabulary Test, Blau Torque Test, and the Rod and Frame Test. Children with reading impairments (n = 24) in all age groups were found to exhibit a marked deficit in the ability to discriminate patterned pairs of tones on the Seashore Rhythm Test compared to controls (n = 26). These children also exhibited deficits in right-left orientation, as indicated by their poor performance on the Blau Torque Test. Performance on the Seashore and the Blau by a group of children diagnosed as learning disabled (n = 9) was similar to the group with reading impairments. No significant differences between controls and children with reading impairments or LD were observed in Rod and Frame or Benton performance. The results suggest that the Seashore Rhythm Test may prove to be a useful tool to detect young children who will later show signs of reading impairment.

Attention↗
PubMedDate not supplied

Comprehension of temporal terms by good and poor readers.

Poor beginning readers often have difficulty comprehending spoken sentences with complex syntactic structures. This study attempts to identify the reasons for this difficulty. Second-grade good and poor readers were tested for comprehension of spoken sentences containing the temporal terms before and after. Processing load was varied systematically while holding syntax constant in an effort to determine whether processing factors contribute to poor readers' comprehension problems, or whether poor readers are simply lacking the structural knowledge required to understand sentences containing temporal terms. The poor readers' high level of performance under conditions of reduced processing demands suggests that their misinterpretations in spoken language understanding may be due, in large part, to limitations in verbal working memory.

Attention↗
PubMed2001

The Mozart effect.

Explore the source record for details and available documents.

Auditory Perception↗
PubMed1998

Human perception of short and long time intervals: its correlation with body temperature and the duration of wake time.

Time estimation was studied in seven human subjects during prolonged sojourn is isolation from time cues. They wore rectal temperature probes throughout the experiments, and during wakefulness recorded each time they thought one hour had passed. At the end of each of these subjective hours they produced a subjective 5 or 10 sec interval. The produced intervals on the 1-h task were not related to body temperature but were correlated with and proportional to the duration of waketime in all subjects. The produced 5 and 10 sec intervals were in all subjects negatively correlated with rectal temperature, but were not associated with wake time. Brief and long time intervals are subjectively experienced via different mechanisms.

Adult↗
PubMed2001

Visuoperceptual impairment in MS patients: nature and possible neural origins.

Failures on visuoperceptual neuropsychological tasks (on neuropsychological tests of visuo-spatial perception or on tests concerning semantic properties of visual objects), may indicate focal deficits of visuoperceptual function, or could be the result of (an)other (peripheral) visual deficit(s), or be the effect of a more general cognitive decline. In multiple sclerosis (MS) patients exhibiting sufficient visual acuity and not showing severe cognitive deterioration, impairment on a comprehensive set of 31 visuoperceptual neuropsychological tasks was compared with spatial resolution deficits (SRD), temporal resolution deficits (TRD) for visual stimuli, abnormal pattern shift visual evoked potential (PSVEP) responses, and failing scores on neuropsychological tasks other than visuoperceptual tasks. Impairment on the visuoperceptual neuropsychological tasks was highly independent from the other abnormal visual and cognitive neurological impairments examined, suggesting that it mostly represented focal deficits. Only TRD in both eyes related to this impairment and this relationship was rather weak. Thus in some MS patients a slowed visual information processing may be one of the combined deficits underlying visuoperceptual neuropsychological task impairment. Given that SRD and TRD were not related to another stage of MS and reflect disturbances of a P (parvocellular channel and ventral stream projections) and M (magnocellular channel and dorsal stream projections) visual-system function respectively, demyelination of a certain M pathway may become a co-determinant of visuoperceptual neuropsychological task impairment more rapidly than damage to a certain P pathway.

Adult↗
PubMed2001

FMRI study relevant to the Mozart effect: brain areas involved in spatial-temporal reasoning.

Behavioral studies, motivated by columnar cortical model predictions, have given evidence for music causally enhancing spatial-temporal reasoning. A wide range of behavioral experiments showed that listening to a Mozart Sonata (K.448) gave subsequent enhancements. An EEG coherence study gave evidence for a carryover from that Mozart Sonata listening condition to the subsequent spatial-temporal task in specific cortical regions. Here we present fMRI studies comparing cortical blood flow activation by the Mozart Sonata vs. other music. In addition to expected temporal cortex activation, we report dramatic statistically significant differences in activation by the Mozart Sonata (in comparison to Beethoven's Fur Elise and 1930s piano music) in dorsolateral pre-frontal cortex, occipital cortex and cerebellum, all expected to be important for spatial-temporal reasoning. It would be of great interest to explicitly test this expectation. We propose an fMRI study comparing (subject by subject) brain areas activated in music listening conditions and in spatial-temporal tasks.

Acoustic Stimulation↗