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PubMed1993

Visual resolution and sensitivity of single cells in the primary visual cortex (V1) of a nocturnal primate (bush baby): correlations with cortical layers and cytochrome oxidase patterns.

1. This study describes the response properties of V1 cortical cells in a nocturnal primate and examines the receptive field organization of these cells in relationship to anatomically defined layers and cytochrome oxidase (CO) rich blobs and CO poor interblob compartments. Visual resolution and contrast sensitivity are consistent with other physiological and behavioral measures in this species. Comparisons are made with response properties of the same zones in macaque monkey, as well as of area 17 of a distantly related species (cat) that also occupies a nocturnal niche. 2. The responses of single cells to drifting sinusoidal gratings were recorded in V1 (striate cortex) of anesthetized, paralyzed bush babies (Galago crassicaudatus). Cells tended to be grouped with respect to ocular dominance, orientation preference, and direction selectivity. There was a high proportion of monocularly driven cells as in macaque monkey. Only 6% of the cells were nonoriented. These were poorly tuned complex cells and bore no resemblance to nonoriented lateral geniculate nucleus (LGN)-like cells reported in layer IV of macaque monkeys. Unidirectional cells were most frequently encountered in cortical layers that receive input from the magnocellular layers of the LGN. 3. Cells were classified as simple (31%) or complex (69%) according to standard criteria. Simple cells were significantly more narrowly tuned than complex cells for both orientation and spatial frequency. Complex cells had significantly higher average optimal spatial frequencies and spatial frequency cutoffs than simple cells. Contrast sensitivity of simple and complex cells averaged 38 and 34, respectively. Spatial resolution and sensitivity of these cells matches behavioral measures in bush baby. The spatial and temporal resolution of bush baby cells are similar to those of cats, which is likely related to the nocturnal niche of both species. 4. Cells in supragranular (I-III) and infragranular (V, VI) layers differed significantly in their response characteristics. The cells in the supragranular layers had significantly higher contrast sensitivity than did the cells in the infragranular layers. Cells in the supragranular layers likewise had higher temporal frequency cutoffs, significantly lower optimal spatial frequencies, lower spatial frequency cutoffs, and tighter orientation tuning than did cells in the infragranular layers. 5. Properties of cells in individual layers and CO blob and interblob compartments also showed differentiation. Layer III had the narrowest orientation and spatial frequency tuning with the tightest tuning in layer IIIC (IVB).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Climbing fiber responses of Purkinje cells to retinal image movement in cat cerebellar flocculus.

1. The complex spike (CS) of the floccular Purkinje cell has been reported to be driven by retinal image movement in the rabbit, the rat, and the monkey, but not yet in the cat, in which the floccular neuronal network is well known. We recorded the CS activity together with concomitant simple spike (SS) activity of the floccular Purkinje cells that responded to large-field visual pattern movement in the anesthetized cat. 2. On the basis of the direction selectivity we divided the cells into two major types: the horizontal type that preferred horizontal stimuli and the vertical type that preferred vertical stimuli. The CS activity of the horizontal-type cell increased during stimuli directed contralaterally to the recording site and decreased during ipsilaterally directed stimuli, whereas that of the vertical-type cell increased during upward stimuli and decreased during downward stimuli. 3. In both types the CS response was larger at lower-velocity stimuli and the response was well maintained at higher-velocity stimuli < or = 180 degrees/s tested. The mean response decline was only 50% at stimulus velocities 90-150 degrees/s compared with the response amplitude at 2 degrees/s stimulus velocity. 4. The majority of the horizontal-type cells were modulated by the stimuli presented to either eye and the dominant eye was ipsilateral to the recording site. The majority of the vertical-type cells were also modulated by the stimuli presented to either eye without obvious differences between two eyes. 5. In both types the receptive field of the ipsilateral eye always included the area centralis and extended widely on both visual hemifields. The receptive field of the contralateral eye also included the area centralis and was usually restricted within the ipsilateral visual hemifield. The stimuli of small visual field (15 degrees x 15 degrees) projecting to the area centralis evoked especially large responses (70% of the full-screen response). 6. The CS and SS responses were reciprocal to each other, that is, when the CS firing increased the SS firing decreased and vice versa. 7. These CS responses are well suited for the direction detection of large-field retinal image motion at a wide velocity range. In light of the present unitary spike data together with the anatomic and eye movement data reported previously, we conclude that the cat flocculus is responsible for reduction of the large-field retinal image motion by producing eye movement in the same direction with the visual motion.

Acceleration↗
PubMed1994

Activity of inferior temporal neurons during orientation discrimination with successively presented gratings.

1. We recorded from inferior temporal (IT) cells in three monkeys while they performed an orientation discrimination task with successively presented gratings. Histological reconstruction of two monkey brains indicated that most recordings were from TE3. The task was exactly the same as the one used in a previous V1 study, allowing direct comparison. 2. One quarter of IT cells were responsive to the grating. Response strength and variability of the cells excited by the grating (n = 341) were similar to those in V1, whereas response latency was on average 40 ms longer than in V1. 3. In one third of the responsive cells orientation had a significant effect. Sensitivity for orientation was captured by the orientation sensitivity index, which ranged from 0 to 0.95 with a median of 0.23. Orientation sensitivity of IT cells was on average much less than that of V1 cells. More cells preferred horizontal and vertical than oblique orientations. 4. The differences in responsiveness and orientation sensitivity among individual animals could be accounted for by the anterior/posterior difference in recording position. 5. Task-related behavioral effects were examined in 283 cells that were responsive to the visual stimuli. Order effects were examined in "same" trials and occurred in half of the IT cells in each of the three monkeys. In these cells there was on average a threefold difference in response between the first stimulus (S1) and the second stimulus in same trials (S2same). In two monkeys the average response to S2same was less than that to S1, whereas in the third monkey the average response to S1 was smaller than that to S2same. 6. IT cells also exhibited same/different effects, whereby response to a physically identical second stimulus differed between same and "different" trials. Generally cells responded more to the second stimulus in different trials than to S2same but the opposite also occurred. For a subset of these cells we could show that the correct/error type of the trial had no effect and that the response occurred before the saccadic response. 7. These context effects were modulations of the gain of the orientation tuning curves for the different types of responses. The tuning for orientation of these different responses was similar. 8. One third of the responsive IT cells exhibited an increased activity in the interstimulus interval (ISI), fitting the definition of delay cells. This activity was maintained when the ISI was lengthened from 300 to 800 ms. The orientation tuning of this response was similar to that for S1 responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Translation invariance in the responses to faces of single neurons in the temporal visual cortical areas of the alert macaque.

1. The responses of single neurons in the inferior temporal cortex and the cortex in the banks of the anterior part of the superior temporal sulcus of three awake, behaving macaques were recorded during a visual fixation task. Stimulus images subtending 17 or 8.5 degrees were presented in the center of the display area, and fixation was either at the center of the display area, or at one of four positions that were on the stimulus, or several degrees off the edge of the test stimulus. The experiments were performed with face-selective cells, and the responses were compared for fixation at each position for both effective and noneffective face stimuli for each cell. 2. The firing rates of most neurons to an effective image did not significantly alter when visual fixation was as far eccentric as the edge of the face, and they showed only a small reduction when the fixation point was up to 4 degrees from the edge of the face. Moreover, stimulus selectivity across faces was maintained throughout this region of the visual field. 3. The centers of the receptive fields of the cells, as shown by the calculated "centers of gravity," were close to the fovea, with almost all being within 3 degrees of the fovea. 4. The receptive fields of the cells typically crossed the vertical midline for at least 5 degrees. 5. Information theory procedures were used to analyze the spike trains of the visual neurons. Nearly six times more information was carried by these neurons' firing rate about the identity of an image than about its position in the visual field. Thus the information theory analysis showed that the responses of these neurons reflected information about which stimulus had been seen in a relatively translation invariant way. 6. Principal component analysis showed that principal component 1 (PC1) is related primarily to firing rate and reflected information primarily about stimulus identity. (For identity PC2 added only 14% more information to that contained in PC1.) Principal component 2 (PC2) was more closely related to neuronal response latencies, which increased with increasing eccentricity of the image in the visual field. PC2 reflected information about the position of the stimulus in the visual field, in that PC2 added 109% more information to that contained in PC1 about the position of the stimulus in the visual field.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Population encoding of spatial frequency, orientation, and color in macaque V1.

1. We recorded local field potentials in the parafoveal representation in the primary visual cortex of anesthetized and paralyzed macaque monkeys with a multicontact electrode that provided for sampling of neural activity at 16 sites along a vertical penetration. Differential recordings at adjacent contacts were transformed into an estimate of current source density (CSD), to provide a measure of local neural activity. 2. We used m-sequence stimuli to map the region of visual space that provided input to the recording site. The local field potential recorded in macaque V1 has a population receptive field (PRF) size of approximately 2 deg2. 3. We assessed spatial tuning by the responses to two-dimensional Gaussian noise, spatially filtered to retain power only within one octave. Responses to achromatic band-limited noise stimuli revealed a prominent band-pass spatial tuning in the upper layers, but a more low-pass spatial tuning in lower layers. 4. We assessed orientation tuning by the responses to band-limited noise whose spectrum was further restricted to lie within 45 degrees wedges. The local field potential showed evidence of orientation tuning at most sites. Orientation tuning in upper and lower layers was manifest by systematic variations not only in response size but also in response dynamics. 5. We assessed chromatic tuning by the responses to isotropic band-limited noise modulated in a variety of directions in tristimulus space. Some lower-layer locations showed a nulling of response under near-isoluminant conditions. However, response dynamics in upper and lower layers depended not only on luminance contrast, but also on chromatic inputs. 6. Responses to near-isoluminant stimuli and to low-contrast luminance modulation were shifted to lower spatial frequencies. 7. We determined the extent to which various temporal frequencies in the response conveyed information concerning spatial frequency, orientation, and color under the steady-state conditions used in these studies. In each case, information is distributed in the response dynamics across a broad temporal frequency range, beginning at 4 Hz (the lowest frequency used). For spatial frequency the information rate remains significant up to at least 25 Hz. For orientation tuning and chromatic tuning, the information rate is lower overall and remains significant up to 13 Hz. In contrast, for texture discrimination, information is shifted to lower temporal frequencies.

Animals↗
PubMed1990

Configuration-sensitive visual responses in the superior colliculus of the house mouse (Mus musculus domesticus).

In order to compare visual pattern discrimination by tectal neurons in distantly related vertebrate groups, collicular cells of mice were examined for their responses to each of three simple configurational stimuli commonly used in studies of amphibians. The stimuli consisted of a large square, a horizontal bar and a vertical bar moved at various velocities. Of the recorded units (n = 51), 30-50% significantly preferred the square to the other stimuli at medium (10 degrees/s) and high (67 degrees/s) velocities. Approximately 10% preferred the horizontal bar at these velocities. A significant discrimination between the horizontal and the vertical bar was found in 39% of the units at a velocity of 10 degrees/s, and in 61% at a velocity of 67 degrees/s. These response types are very similar to those found in amphibians; therefore, it is concluded that tectal configurational sensitivity may be a plesiomorphic tetrapod character resulting from basic properties of tectal neuronal circuitry.

Animals↗
PubMed1988

Visual involvement in Friedreich's ataxia: PERG and VEP study.

Neuro-ophthalmological assessment, including red-free light retinography, in conjunction with simultaneous visual evoked potential (VEP) and pattern electroretinogram (PERG) recordings were performed in 10 Friedreich's ataxia patients: 9 patients showed marked VEP abnormalities. Moderate PERG amplitude reduction, with normal latencies, was related to mild and scattered fiber loss revealed by red-free light retinography. The initial part of the visual pathways does not seem to be the main site of electrophysiological abnormalities as demonstrated by the greater extent and relative independence of VEP versus PERG alterations. Primary axonal degeneration of the optic nerve and tracts cannot account for all features of VEP abnormalities, thus implying some dysfunction in succeeding visual structures as well.

Adolescent↗
PubMed1987

Rapid information processing and concomitant event-related brain potentials in smokers differing in CO absorption.

The present study relates subject-paced rapid information processing to different components of event-related brain potentials in an attempt to gain more information about changes in mental performance in relation to alveolar smoke absorption as assessed by expired air CO measurement. The task consisted in the presentation of pseudorandom sequences of single digits, and the subjects had to respond to each sequence of three odd or three even digits. The triplets evoked a typical late negativity in the event-related potential between the second and third digit as well as a P300 component following the third digit. In 21 smokers, task performance, event-related potentials and tidal air CO concentration were measured before and after smoking a cigarette. The results revealed increases in performance and P300 magnitude from pre- to postsmoking which were unaffected by the amount of CO absorption. A differential trend was seen, however, with the late negativity, which increased from pre- to postsmoking only in subjects with a large amount of CO absorption. The results support the assumption of the distraction arousal model used as an interpretation of these effects on contingent negative variation and suggest that high CO absorbing smokers possibly depend more on neuropharmacological effects of smoking than smokers with a low amount of CO absorption.

Adolescent↗
PubMed1993

[Influence of Long-Term Stimulation on Pattern-Reversal Visual Evoked Cortical Potentials].

In 20 subjects, we recorded the pattern-reversal visual evoked cortical potential (VECP) over a period of 30 min. We could not find any remarkable alterations of the peak times, they were unchanged over the time. During the first 10 min, the amplitudes showed a clear tendency to decrease if one evaluated the averaging value of the whole group. After this time, there were no significant changes. But we learned a quite different behavior of amplitudes evaluating the record of each subject. We found 5 types of different behavioral modulated responses. The problems of long-term investigation are sophisticated and need further investigation to learn which different factors have an impact on VECP. From a clinical point of view, a long-term investigation shows no relevant potential alterations.

Adult↗
PubMed1999

Firing rate distributions and efficiency of information transmission of inferior temporal cortex neurons to natural visual stimuli.

The distribution of responses of sensory neurons to ecological stimulation has been proposed to be designed to maximize information transmission, which according to a simple model would imply an exponential distribution of spike counts in a given time window. We have used recordings from inferior temporal cortex neurons responding to quasi-natural visual stimulation (presented using a video of everyday lab scenes and a large number of static images of faces and natural scenes) to assess the validity of this exponential model and to develop an alternative simple model of spike count distributions. We find that the exponential model has to be rejected in 84% of cases (at the p < 0.01 level). A new model, which accounts for the firing rate distribution found in terms of slow and fast variability in the inputs that produce neuronal activation, is rejected statistically in only 16% of cases. Finally, we show that the neurons are moderately efficient at transmitting information but not optimally efficient.

Animals↗
PubMed2006

Electrophysiological correlates of similarity-based interference during detection of visual forms.

Illusory figure completion demonstrates the ability of the visual system to integrate information across gaps. Mechanisms that underlie figural emergence support the interpolation of contours and the filling-in of form information [Grossberg, S., & Mingolla, E. Neural dynamics of form perception: Boundary completion, illusory figures and neon colour spreading. Psychological Review, 92, 173-211, 1985]. Although both processes contribute to figure formation, visual search for an illusory target configuration has been shown to be susceptible to interfering form, but not contour, information [Conci, M., Müller, H. J., & Elliott, M. A. The contrasting impact of global and local object attributes on Kanizsa figure detection. Submitted]. Here, the physiological basis of form interference was investigated by recording event-related potentials elicited from contour- and surface-based distracter interactions with detection of a target Kanizsa figure. The results replicated the finding of form interference and revealed selection of the target and successful suppression of the irrelevant distracter to be reflected by amplitude differences in the N2pc component (240-340 msec). In conclusion, the observed component variations reflect processes of target selection on the basis of integrated form information resulting from figural completion processes.

Adult↗
PubMed2002

Temporal dynamics of the human response to symmetry.

Symmetry is a highly salient feature of animals, plants, and the constructed environment. Although the perceptual phenomenology of symmetry processing is well understood, little is known about the underlying neural mechanisms. Here we use visual evoked potentials to measure the time course of neural events associated with the extraction of symmetry in random dot fields. We presented sparse random dot patterns that were symmetric about both the vertical and horizontal axes. Symmetric patterns were alternated with random patterns of the same density every 500 msec, using new exemplars of symmetric and random patterns on each image update. Random/random exchanges were used as a control. The response to updates of random patterns was multiphasic, consisting of P65, N90, P110, N140 and P220 peaks. The response to symmetric/random sequences was indistinguishable from that for random/random sequences up to about 220 msec, after which the response to symmetric patterns became relatively more negative. Symmetry in random dot patterns thus appears to be extracted after an initial response phase that is indifferent to configuration. These results are consistent with the hypothesis (Lee, Mumford, Romero, & Lamme, 1998; Tyler & Baseler, 1998) that the symmetry property is extracted by processing in extrastriate cortex.

Adult↗
PubMedDate not supplied

P300 and reaction time in Parkinson's disease.

The event-related potential and motor reaction time were simultaneously recorded in 35 patients with Parkinson's disease (26 nondemented and nine demented) and 15 age-matched neurologically normal control subjects during the performance of visual discrimination tasks. There were no significant differences in either the latency or amplitude of the P300 component between the nondemented patients and the control subjects, but the patients with nondemented Parkinson's disease had a significantly prolonged reaction time compared with the controls. In patients with demented Parkinson's disease, both P300 latency and reaction time were significantly prolonged compared with the normal controls. These results suggest that response selection and execution are impaired in patients with nondemented Parkinson's disease, although the stimulus evaluation process is largely preserved, whereas patients with demented Parkinson's disease have impairment of stimulus evaluation, go/no-go response selection, and execution.

Aged↗
PubMed1981

Some electrophysiological observations in obsessional states.

Averaged evoked potentials were recorded from a group of obsessional patients and matched normal controls for three types of visual stimulation: passive monitoring of a light flash, a pattern consisting of gratings and a cognitive task involving discrimination of two similar shapes. As the complexity of information processing required by the tasks increased, differences in the evoked potentials of obsessionals became more marked. The main finding was of faster latency and reduced amplitude of the N220 component in the cognitive task. The relevance of this finding to a theory of obsessional disorder is discussed.

Adult↗
PubMed1983

Further observations of evoked potentials in obsessional patients.

This study was designed to replicate and extend earlier findings. Evoked potentials (EP) were recorded, using a task of varying complexity involving shape discrimination, with matched groups of obsessional and normal subjects. Results confirmed previous findings that obsessional patients are characterized by reduced amplitudes and decreased latencies of late EP components; divergences between the groups were more marked for tasks of increased complexity.

Adult↗
PubMed1983

Abnormal visual evoked potentials in myotonic dystrophy.

Pattern-shift visual evoked potentials (VEPs) were recorded in 17 patients with myotonic dystrophy. Abnormalities of latency or amplitude were found in 10 patients (59%) with no obvious retinal or other significant ocular abnormality. All patients had a visual acuity of 20/30 or better. Since most patients had bilateral VEP abnormalities, localization of the disturbance was not certain.

Adult↗
PubMed1985

Pattern evoked potentials (PEPs) in Parkinson's disease.

Controversy exists in the literature concerning whether Parkinson's disease (PD) results in prolongation of pattern evoked potential (PEP) responses. PEPs were obtained in 20 patients with PD. The latencies of the first major positive potential (P2) in response to independent left and right eye stimulation were evaluated. There was no statistically significant difference (group or individual) when patients with PD were compared with age-corrected controls. There was no difference in results in comparing patients with mild, moderate, and severe PD. These results contradict previous reports of markedly abnormal PEPs.

Aged↗