Saccade-related activity in the lateral intraparietal area. I. Temporal properties; comparison with area 7a

1. The cortex of the inferior parietal lobule (IPL) contains neurons whose activity is related to saccadic eye movements. The exact role of the IPL in relation to saccades remains, however, unclear. In this and the companion paper, we approach this problem by quantifying many of the spatial and temporal parameters of the saccade-related (S) activity. These parameters have hitherto been largely unstudied. 2. The activity of single neurons was recorded from Macaca mulatta monkeys while they were performing a delayed-saccade task. The analysis presented here is based on 161 neurons recorded from the lateral intraparietal area (LIP), a recently defined subdivision of the IPL; and 54 neurons recorded from the neighboring part of the IPL, area 7a. Overall, 409 IPL neurons were isolated in this study. 3. The typical activity of IPL neurons during the delayed-saccade task has three basic phases: light sensitive (LS), memory (M), and S. These basic phases are common to neurons of both areas LIP and 7a. In each phase (LS, M, and S), individual neurons may or may not be active. Most LIP neurons, however, are active in more than one phase. 4. To compare the activity levels of different neurons, the actual firing rate was weighted by each neuron's background level, yielding an "activity index" for each neuron, in each phase of the task. We calculated the activity index for the LS and M phases and for three phases related to the saccade: a presaccadic (Pre-S), a saccade-coincident (S-Co), and a postsaccadic (Post-S) phase. For area LIP neurons the median values of the activity index were high for the LS, M, Pre-S, and S-Co activities, and slightly lower in the Post-S period. In area 7a the median values were low for the LS phase and, in particular, for the M and Pre-S phases, somewhat higher coincident with the saccade, and high post-saccadically. 5. In area LIP, in each phase, 49-63% of the neurons had excitatory activity, and 10-17% had inhibitory responses. 6. In contrast, in area 7a excitatory responses were most frequent in the Post-S phase (56%). Excitation was particularly infrequent during M (28%) and Pre-S (22%). The incidence of inhibitory responses varied too (4-18%). The time course of inhibition was roughly opposite that of excitation; the highest frequency of inhibitory responses occurred during the saccade.(ABSTRACT TRUNCATED AT 400 WORDS)

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Direction Selectivity of Neurons in the Macaque Lateral Intraparietal Area

Journal of Neurophysiology ◽

10.1152/jn.00400.2007 ◽

2009 ◽

Vol 101 (1) ◽

pp. 289-305 ◽

Cited By ~ 43

Author(s):

Alessandra Fanini ◽

John A. Assad

Keyword(s):

Saccadic Eye Movements ◽

Spatial Location ◽

Direction Selectivity ◽

Average Strength ◽

Visual Stream ◽

Lateral Intraparietal Area ◽

Cortical Areas ◽

Saccade Task ◽

Direction Tuning ◽

Dorsal Visual Stream

The lateral intraparietal area (LIP) of the macaque is believed to play a role in the allocation of attention and the plan to make saccadic eye movements. Many studies have shown that LIP neurons generally encode the static spatial location demarked by the receptive field (RF). LIP neurons might also provide information about the features of visual stimuli within the RF. For example, LIP receives input from cortical areas in the dorsal visual pathway that contain many direction-selective neurons. Here we examine direction selectivity of LIP neurons. Animals were only required to fixate while motion stimuli appeared in the RF. To avoid spatial confounds, the motion stimuli were patches of randomly arrayed dots that moved with 100% coherence in eight different directions. We found that the majority (61%) of LIP neurons were direction selective. The direction tuning was fairly broad, with a median direction-tuning bandwidth of 136°. The average strength of direction selectivity was weaker in LIP than that of other areas of the dorsal visual stream but that difference may be because of the fact that LIP neurons showed a tonic offset in firing whenever a visual stimulus was in the RF, independent of direction. Direction-selective neurons do not seem to constitute a functionally distinct subdivision within LIP, because those neurons had robust, sustained delay-period activity during a memory delayed saccade task. The direction selectivity could also not be explained by asymmetries in the spatial RF, in the hypothetical case that the animals attended to slightly different locations depending on the direction of motion in the RF. Our results show that direction selectivity is a distinct attribute of LIP neurons in addition to spatial encoding.

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Motor intention activity in the macaque's lateral intraparietal area. I. Dissociation of motor plan from sensory memory

Journal of Neurophysiology ◽

10.1152/jn.1996.76.3.1439 ◽

1996 ◽

Vol 76 (3) ◽

pp. 1439-1456 ◽

Cited By ~ 126

Author(s):

P. Mazzoni ◽

R. M. Bracewell ◽

S. Barash ◽

R. A. Andersen

Keyword(s):

Eye Movements ◽

Visual Stimulus ◽

Visual Stimuli ◽

Saccadic Eye Movements ◽

Stimulus Location ◽

Sensory Memory ◽

Lateral Intraparietal Area ◽

Preferred Direction ◽

Motor Plan ◽

Stimulation Of

1. The lateral intraparietal area (area LIP) of the monkey's posterior parietal cortex (PPC) contains neurons that are active during saccadic eye movements. These neurons' activity includes visual and saccade-related components. These responses are spatially tuned and the location of a neuron's visual receptive field (RF) relative to the fovea generally overlaps its preferred saccade amplitude and direction (i.e., its motor field, MF). When a delay is imposed between the presentation of a visual stimulus and a saccade made to its location (memory saccade task), many LIP neurons maintain elevated activity during the delay (memory activity, M), which appears to encode the metrics of the next intended saccadic eye movements. Recent studies have alternatively suggested that LIP neurons encode the locations of visual stimuli regardless of where the animal intends to look. We examined whether the M activity of LIP neurons specifically encodes movement intention or the locations of recent visual stimuli, or a combination of both. In the accompanying study, we investigated whether the intended-movement activity reflects changes in motor plan. 2. We trained monkeys (Macaca mulatta) to memorize the locations of two visual stimuli and plan a sequence of two saccades, one to each remembered target, as we recorded the activity of single LIP neurons. Two targets were flashed briefly while the monkey maintained fixation; after a delay the fixation point was extinguished, and the monkey made two saccades in sequence to each target's remembered location, in the order in which the targets were presented. This "delayed double saccade" (DDS) paradigm allowed us to dissociate the location of visual stimulation from the direction of the planned saccade and thus distinguish neuronal activity related to the target's location from activity related to the saccade plan. By imposing a delay, we eliminated the confounding effect of any phasic responses coincident with the appearance of the stimulus and with the saccade. 3. We arranged the two visual stimuli so that in one set of conditions at least the first one was in the neuron's visual RF, and thus the first saccade was in the neuron's motor field (MF). M activity should be high in these conditions according to both the sensory memory and motor plan hypotheses. In another set of conditions, the second stimulus appeared in the RF but the first one was presented outside the RF, instructing the monkey to plan the first saccade away from the neuron's MF. If the M activity encodes the motor plan, it should be low in these conditions, reflecting the plan for the first saccade (away from the MF). If it is a sensory trace of the stimulus' location, it should be high, reflecting stimulation of the RF by the second target. 4. We tested 49 LIP neurons (in 3 hemispheres of 2 monkeys) with M activity on the DDS task. Of these, 38 (77%) had M activity related to the next intended saccade. They were active in the delay period, as expected, if the first saccade was in their preferred direction. They were less active or silent if the next saccade was not in their preferred direction, even when the second stimulus appeared in their RF. 5. The M activity of 8 (16%) of the remaining neurons specifically encoded the location of the most recent visual stimulus. Their firing rate during the delay reflected stimulation of the RF independently of the saccade being planned. The remaining 3 neurons had M activity that did not consistently encode either the next saccade or the stimulus' location. 6. We also recorded the activity of a subset of neurons (n = 38) in a condition in which no stimulus appeared in a neuron's RF, but the second saccade was in the neuron's MF. In this case the majority of neurons tested (23/38, 60%) became active in the period between the first and second saccade, even if neither stimulus had appeared in their RF. Moreover, this activity appeared only after the first saccade had started in all but two of

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Detection of G1 proteins in Chinese hamster cells synchronized by isoleucine deprivation or mitotic selection.

The Journal of Cell Biology ◽

10.1083/jcb.66.1.95 ◽

1975 ◽

Vol 66 (1) ◽

pp. 95-101 ◽

Cited By ~ 13

Author(s):

K D Ley

Keyword(s):

Time Course ◽

Sodium Dodecyl ◽

Chinese Hamster ◽

Protein S ◽

S Phase ◽

Supernatant Fraction ◽

G1 Phase ◽

Differential Centrifugation ◽

Chinese Hamster Cells ◽

Soluble Supernatant

Examination of labeling patterns of proteins in Chinese hamster cells(line CHO) revealed the presence of a class of protein(s) that is synthesized during G1 phase of the cell cycle. Cells arrested in G1 by isoleucine (Ile) deprivation were prelabeded with [14-C]Ile, induced to traverse G1 by addition of unlabeled Ile, and labeled with [3-H]Ile at hourly intervals. Cells were fractionated into neclear and cytoplasmic portions, and proteins were separated by sodium dodecyl sulfate-polyacrylamide get electrophoresis. Gel profiles of proteins in the 45,000-160,000 mol wt range from the cytoplasm of cells in G1 were similar to those from cells arrested in G1 except for the presence of a mojor peak of [1-H]Ile incorporated into a protein(s) of approximately 80,000 mol wt. Peaks of net [3-H]Ile incorporation were not detected in neclear preparations. Cellular fractionation by differential centrifugation showed the peak I protein was located in the soluble supernatant fraction of the cytoplasm. Time-course studies showed that synthesis of this protein began 1-2 h after initiation of G1 traverse; the protein reached maximum levels in 4-6 h and was reduced to undetectable levels by 9 h. A cytoplasmic protein with similar electrophoretic mobility was found in G1 phase of cells synchronized by mitotic selection. This class of proteins is synthesized by cells before entry into S phase and may be involved in initiation of DNA synthesis.

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The Solar Twin Planet Search

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629294 ◽

2018 ◽

Vol 619 ◽

pp. A73 ◽

Cited By ~ 21

Author(s):

Diego Lorenzo-Oliveira ◽

Fabrício C. Freitas ◽

Jorge Meléndez ◽

Megan Bedell ◽

Iván Ramírez ◽

...

Keyword(s):

Solar Activity ◽

Activity Index ◽

Open Clusters ◽

Activity Level ◽

Age Dating ◽

Physical Parameters ◽

Activity Levels ◽

Sharp Drop ◽

Activity Diagram ◽

Activity Indices

Context. It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1–2 Gyr that is followed by a relatively inactive constant phase. Aims. We revisited the activity-age relation using time-series observations of a large sample of solar twins whose precise isochronal ages and other important physical parameters have been determined. Methods. We measured the Ca II H and K activity indices using ≈9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale (SMW), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of Teff, and then computed an improved bolometric flux normalized activity index log R′HK (Teff) for the entire sample. Results. New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using log R′HK (Teff). We measured an average solar activity of SMW = 0.1712 ± 0.0017 during solar magnetic cycles 23–24 covered by HARPS observations, and we also inferred an average of SMW = 0.1694 ± 0.0025 for cycles 10–24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6–7 Gyr, in agreement with previous works using open clusters and field stars with precise ages. Conclusions. Our research confirms that Ca II H & K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6–7 Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations effects. The Sun seems to have a normal activity level and variability for its age.

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GABAA-Mediated IPSCs in Piriform Cortex Have Fast and Slow Components With Different Properties and Locations on Pyramidal Cells

Journal of Neurophysiology ◽

10.1152/jn.1997.78.5.2531 ◽

1997 ◽

Vol 78 (5) ◽

pp. 2531-2545 ◽

Cited By ~ 49

Author(s):

A. Kapur ◽

R. A. Pearce ◽

W. W. Lytton ◽

L. B. Haberly

Keyword(s):

Time Course ◽

Feedback Inhibition ◽

Slow Component ◽

Piriform Cortex ◽

Pyramidal Cells ◽

Long Term Potentiation ◽

Companion Paper ◽

Protective Role ◽

Functional Roles ◽

Term Potentiation

Kapur, A., R. A. Pearce, W. W. Lytton, and L. B. Haberly.GABAA-mediated IPSCs in piriform cortex have fast and slow components with different properties and locations on pyramidal cells. J. Neurophysiol. 78: 2531–2545, 1997. A recent study in piriform (olfactory) cortex provided evidence that, as in hippocampus and neocortex, γ-aminobutyric acid-A (GABAA)-mediated inhibition is generated in dendrites of pyramidal cells, not just in the somatic region as previously believed. This study examines selected properties of GABAA inhibitory postsynaptic currents (IPSCs) in dendritic and somatic regions that could provide insight into their functional roles. Pharmacologically isolated GABAA-mediated IPSCs were studied by whole cell patch recording in slices. To compare properties of IPSCs in distal dendritic and somatic regions, local stimulation was carried out with tungsten microelectrodes, and spatially restricted blockade of GABAA-mediated inhibition was achieved by pressure-ejection of bicuculline from micropipettes. The results revealed that largely independent circuits generate GABAA inhibition in distal apical dendritic and somatic regions. With such independence, a selective decrease in dendritic-region inhibition could enhance integrative or plastic processes in dendrites while allowing feedback inhibition in the somatic region to restrain system excitability. This could allow modulatory fiber systems from the basal forebrain or brain stem, for example, to change the functional state of the cortex by altering the excitability of interneurons that mediate dendritic inhibition without increasing the propensity for regenerative bursting in this highly epileptogenic system. As in hippocampus, GABAA-mediated IPSCs were found to have fast and slow components with time constants of decay on the order of 10 and 40 ms, respectively, at 29°C. Modeling analysis supported physiological evidence that the slow time constant represents a true IPSC component rather than an artifactual slowing of the fast component from voltage clamp of a dendritic current. The results indicated that, whereas both dendritic and somatic-region IPSCs have both fast and slow GABAA components, there is a greater proportion of the slow component in dendrites. In a companion paper, the hypothesis is explored that the resulting slower time course of the dendritic IPSC increases its capacity to regulate the N-methyl-d-aspartate component of EPSPs. Finally, evidence is presented that the slow GABAA-mediated IPSC component is regulated by presynaptic GABAB inhibition whereas the fast is not. Based on the requirement for presynaptic GABAB-mediated block of inhibition for expression of long-term potentiation, this finding is consistent with participation of the slow GABAA component in regulation of synaptic plasticity. The lack of susceptibility of the fast GABAA component to the long-lasting, activity-induced suppression mediated by presynaptic GABAB receptors is consistent with a protective role for this process in preventing seizure activity.

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A Radioautographic Study of the time Course of Male Meiosis in the Newt Triturus Vulgaris

Journal of Cell Science ◽

10.1242/jcs.3.4.615 ◽

1968 ◽

Vol 3 (4) ◽

pp. 615-626

Author(s):

H. G. CALLAN ◽

J. H. TAYLOR

Keyword(s):

Time Course ◽

Male Meiosis ◽

S Phase ◽

Triturus Vulgaris ◽

Random Segregation ◽

Label Distribution

In male Triturus vulgaris at 16 °C the pre-meiotic synthesis of DNA (S-phase) takes 9-10 days. The S-phase starts 1-2 days after completion of the ultimate spermatogonial mitosis, and extends into leptotene. Heterochromatic regions, most of which lie close to the centromeres, start and finish replicating about 1 day later than other parts of the chromosomes. Synapsis starts 6 days after the end of pre-meiotic S and is completed 8 days later. Pachytene lasts for 4 or 5 days, diplotene for 1 or 2 days, and first metaphase occurs 20 or 21 days after the end of pre-meiotic S. Label distribution at first metaphase in spermatocytes stemming from spermatogonia which incorporated [3H]thymidine during the penultimate intermitotic S shows that random segregation and assortment of labelled and unlabelled chromatids took place at the ultimate spermatogonial mitosis.

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Physical Activity in Preschool Children With the Transition to Outdoors

Journal of Physical Activity and Health ◽

10.1123/jpah.10.2.170 ◽

2013 ◽

Vol 10 (2) ◽

pp. 170-175 ◽

Cited By ~ 22

Author(s):

Russell R. Pate ◽

Marsha Dowda ◽

William H. Brown ◽

Jonathan Mitchell ◽

Cheryl Addy

Keyword(s):

Physical Activity ◽

Time Course ◽

Outdoor Play ◽

Activity Levels ◽

Physically Active ◽

Minute Period ◽

Physical Activity Levels ◽

Trained Observers ◽

Children’S Physical Activity ◽

Observation Period

Background:It is known that children are more physically active outdoors than indoors. However, few previous studies have observed the time course for physical activity as young children transition from indoor to outdoor activities.Methods:Participants were 3- to 5-year-old children enrolled in the Children’s Activity and Movement in Preschool Study (CHAMPS). Trained observers used the Observational System for Recording Physical Activity in Children-Preschool Version (OSRAC-P) to record children’s physical activity levels over 20 minutes in outdoor settings. The 20-minute outdoor observational period began immediately following the transition from indoors to outdoors.Results:Children’s activity levels were moderately high at the time of transition and declined over the 20-minute observation period. Different patterns, however, were observed for boys and girls. Overall, boys were more active than girls. Boys’ activity levels declined in a linear fashion over the 20-minute period, while girls’ activity levels increased slightly, decreased, and then increased slightly again.Conclusions:These data indicate that physical activity levels decline with increased duration of outdoor play. The frequency and duration of outdoor play should be investigated for the purpose of optimizing physical activity levels.

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Differential Regulation of P27Kip1 Expression by Mitogenic and Hypertrophic Factors

The Journal of Cell Biology ◽

10.1083/jcb.148.3.543 ◽

2000 ◽

Vol 148 (3) ◽

pp. 543-556 ◽

Cited By ~ 97

Author(s):

Marc J. Servant ◽

Philippe Coulombe ◽

Benjamin Turgeon ◽

Sylvain Meloche

Keyword(s):

Growth Factor ◽

Time Course ◽

Transforming Growth Factor ◽

Transforming Growth Factor Β1 ◽

S Phase ◽

Ang Ii ◽

Differential Growth ◽

Mrna Accumulation ◽

P27kip1 Expression ◽

Cellular Hypertrophy

Platelet-derived growth factor-BB (PDGF-BB) acts as a full mitogen for cultured aortic smooth muscle cells (SMC), promoting DNA synthesis and cell proliferation. In contrast, angiotensin II (Ang II) induces cellular hypertrophy as a result of increased protein synthesis, but is unable to drive cells into S phase. In an effort to understand the molecular basis for this differential growth response, we have examined the downstream effects of PDGF-BB and Ang II on regulators of the cell cycle machinery in rat aortic SMC. Both PDGF-BB and Ang II were found to stimulate the accumulation of G1 cyclins with similar kinetics. In addition, little difference was observed in the expression level of their catalytic partners, Cdk4 and Cdk2. However, while both factors increased the enzymatic activity of Cdk4, only PDGF-BB stimulated Cdk2 activity in late G1 phase. The lack of activation of Cdk2 in Ang II-treated cells was causally related to the failure of Ang II to stimulate phosphorylation of the enzyme on threonine and to downregulate p27Kip1 expression. By contrast, exposure to PDGF-BB resulted in a progressive and dramatic reduction in the level of p27Kip1 protein. The time course of p27Kip1 decline was correlated with a reduced rate of synthesis and an increased rate of degradation of the protein. Importantly, the repression of p27Kip1 synthesis by PDGF-BB was associated with a marked attenuation of Kip1 gene transcription and a corresponding decrease in Kip1 mRNA accumulation. We also show that the failure of Ang II to promote S phase entry is not related to the autocrine production of transforming growth factor-β1 by aortic SMC. These results identify p27Kip1 as an important regulator of the phenotypic response of vascular SMC to mitogenic and hypertrophic stimuli.

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Time course of spatiotopic updating across saccades

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1812210116 ◽

2019 ◽

Vol 116 (6) ◽

pp. 2027-2032 ◽

Cited By ~ 6

Author(s):

Jasper H. Fabius ◽

Alessio Fracasso ◽

Tanja C. W. Nijboer ◽

Stefan Van der Stigchel

Keyword(s):

Eye Movements ◽

Visual System ◽

Eye Movement ◽

Time Course ◽

Saccadic Eye Movements ◽

Oculomotor System ◽

Stimulus Onset ◽

Oculomotor Behavior ◽

Behavioral Studies ◽

The Brain

Humans move their eyes several times per second, yet we perceive the outside world as continuous despite the sudden disruptions created by each eye movement. To date, the mechanism that the brain employs to achieve visual continuity across eye movements remains unclear. While it has been proposed that the oculomotor system quickly updates and informs the visual system about the upcoming eye movement, behavioral studies investigating the time course of this updating suggest the involvement of a slow mechanism, estimated to take more than 500 ms to operate effectively. This is a surprisingly slow estimate, because both the visual system and the oculomotor system process information faster. If spatiotopic updating is indeed this slow, it cannot contribute to perceptual continuity, because it is outside the temporal regime of typical oculomotor behavior. Here, we argue that the behavioral paradigms that have been used previously are suboptimal to measure the speed of spatiotopic updating. In this study, we used a fast gaze-contingent paradigm, using high phi as a continuous stimulus across eye movements. We observed fast spatiotopic updating within 150 ms after stimulus onset. The results suggest the involvement of a fast updating mechanism that predictively influences visual perception after an eye movement. The temporal characteristics of this mechanism are compatible with the rate at which saccadic eye movements are typically observed in natural viewing.

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