Changing the angular separation between two visual stimuli attached to the wall of a recording cylinder causes the firing fields of place cells to move relative to each other, as though the representation of the floor undergoes a topological distortion. The displacement of the firing field center of each cell is a vector whose length is equal to the linear displacement and whose angle indicates the direction that the field center moves in the environment. Based on the observation that neighboring fields move in similar ways, whereas widely separated fields tend to move relative to each other, we develop an empirical vector-field model that accounts for the stated effects of changing the card separation. We then go on to show that the same vector-field equation predicts additional aspects of the experimental results. In one example, we demonstrate that place cell firing fields undergo distortions of shape after the card separation is changed, as though different parts of the same field are affected by the stimulus constellation in the same fashion as fields at different locations. We conclude that the vector-field formalism reflects the organization of the place-cell representation of the environment for the current case, and through suitable modification may be very useful for describing motions of firing patterns induced by a wide variety of stimulus manipulations.

• MeSH
• akční potenciály fyziologie   MeSH
• hipokampus cytologie   fyziologie   MeSH
• interneurony fyziologie   MeSH
• krysa rodu Rattus MeSH
• mapování mozku MeSH
• modely neurologické * MeSH
• světelná stimulace MeSH
• vnímání prostoru fyziologie   MeSH
• zraková pole fyziologie   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu Rattus MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Research Support, U.S. Gov't, P.H.S. MeSH

Photosynthetic organisms exposed to a dynamic light environment exhibit complex transients of photosynthetic activities that are strongly dependent on the temporal pattern of the incident irradiance. In a harmonically modulated light of intensity I approximately const.+sin(omegat), chlorophyll fluorescence response consists of a steady-state component, a component modulated with the angular frequency of the irradiance omega and several upper harmonic components (2omega, 3omega and higher). Our earlier reverse engineering analysis suggests that the non-linear response can be caused by a negative feedback regulation of photosynthesis. Here, we present experimental evidence that the negative feedback regulation of the energetic coupling between phycobilisome and Photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC6803 indeed results in the appearance of upper harmonic modes in the chlorophyll fluorescence emission. Dynamic changes in the coupling of the phycobilisome to PSII are not accompanied by corresponding antiparallel changes in the Photosystem I (PSI) excitation, suggesting a regulation limited to PSII. Strong upper harmonic modes were also found in the kinetics of the non-photochemical quenching (NPQ) of chlorophyll fluorescence, of the P700 redox state and of the CO(2) assimilation in tobacco (Nicotiana tabaccum) exposed to harmonically modulated light. They are ascribed to negative feedback regulation of the reactions of the Calvin-Benson cycle limiting the photosynthetic electron transport. We propose that the observed non-linear response of photosynthesis may also be relevant in a natural light environment that is modulated, e.g., by ocean waves, moving canopy or by varying cloud cover. Under controlled laboratory conditions, the non-linear photosynthetic response provides a new insight into dynamics of the regulatory processes.

• MeSH
• chlorofyl metabolismus   MeSH
• fotosystém II (proteinový komplex) fyziologie   účinky záření   MeSH
• fykobilizomy fyziologie   účinky záření   MeSH
• fyziologická adaptace fyziologie   účinky záření   MeSH
• homeostáza fyziologie   účinky záření   MeSH
• listy rostlin fyziologie   účinky záření   MeSH
• nelineární dynamika MeSH
• oscilometrie metody   MeSH
• periodicita MeSH
• sinice fyziologie   účinky záření   MeSH
• světelná stimulace metody   MeSH
• světlo MeSH
• tabák fyziologie   účinky záření   MeSH
• tma MeSH
• zpětná vazba * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH
• Názvy látek
• chlorofyl MeSH
• fotosystém II (proteinový komplex) MeSH
• fykobilizomy MeSH

The visual sensory system is essential for animals to perceive their environment and is thus under strong selection. In aquatic environments, light intensity and spectrum differ primarily along a depth gradient. Rhodopsin (RH1) is the only opsin responsible for dim-light vision in vertebrates and has been shown to evolve in response to the respective light conditions, including along a water depth gradient in fishes. In this study, we examined the diversity and sequence evolution of RH1 in virtually the entire adaptive radiation of cichlid fishes in Lake Tanganyika, focusing on adaptations to the environmental light with respect to depth. We show that Tanganyikan cichlid genomes contain a single copy of RH1. The 76 variable amino acid sites detected in RH1 across the radiation were not uniformly distributed along the protein sequence, and 31 of these variable sites show signals of positive selection. Moreover, the amino acid substitutions at 15 positively selected sites appeared to be depth-related, including three key tuning sites that directly mediate shifts in the peak spectral sensitivity, one site involved in protein stability and 11 sites that may be functionally important on the basis of their physicochemical properties. Among the strongest candidate sites for deep-water adaptations are two known key tuning sites (positions 292 and 299) and three newly identified variable sites (37, 104 and 290). Our study, which is the first comprehensive analysis of RH1 evolution in a massive adaptive radiation of cichlid fishes, provides novel insights into the evolution of RH1 in a freshwater environment.

• Klíčová slova
• freshwater fish, opsin, photic environment, rod photoreceptor, spectral tuning, vision,
• MeSH
• cichlidy * genetika   MeSH
• fylogeneze MeSH
• jezera MeSH
• molekulární evoluce MeSH
• rodopsin genetika   MeSH
• ryby MeSH
• voda MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Tanzanie MeSH
• Názvy látek
• rodopsin MeSH
• voda MeSH

Animals often demonstrate the ability to use the geometric configuration of multiple landmarks for orientation in the environment. We developed a new behavioral task using a computer screen for presentation of visual stimuli allowing the rats to make navigational decisions in real space according to the geometric configuration of external virtual patterns (designed as a possible representation of this space). The rats were placed in a Skinner box with four nosing holes in the transparent front wall through which the computer screen was visible. They were trained in successive phases: first the visual stimulus displayed on the screen directly marked the rewarded nosing hole, then the displayed stimuli were reduced in size or displaced, thus disconnected from the response space. The results suggested that rats were able to use the geometric configuration of stimuli presented on the computer screen for navigational decisions in real space.

• MeSH
• krysa rodu Rattus MeSH
• orientace fyziologie   MeSH
• počítačová grafika MeSH
• podněty MeSH
• potkani Long-Evans MeSH
• rozhodování fyziologie   MeSH
• světelná stimulace MeSH
• vnímání prostoru fyziologie   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu Rattus MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

In earlier experiments we have demonstrated that macaque monkeys (Macaca mulatta) are able to use abstract visual stimuli presented on a computer screen to make spatial choices in the real environment. In those experiments a touch board ("response space") was directly connected to the computer screen ("virtual space"). The goal of the present experiment was to find out whether macaque monkeys are able: (1) To make spatial choices in a response space which is completely separated from the screen where the stimuli (designed as representation of the response space) are presented. (2) To make spatial choices based on visual stimuli representing the configuration of the response space which are rotated with respect to this response space. The monkeys were trained to choose one of the nine "touch holes" on a transparent touch panel situated beside a computer monitor on which the visual stimuli were presented. The visual stimuli were designed as an abstract representation of the response space: the rewarded position was shown as a bright circle situated at a certain position in the rectangle representing the contours of the touch panel. At first, the monkeys were trained with non-rotated spatial stimuli. After this initial training, the visual stimuli were gradually rotated by 20 degrees in each step. In the last phase, the stimulus was suddenly rotated in the opposite direction by 60 degrees in one step. The results of the experiment suggest that the monkeys are able to use successfully abstract stimuli from one spatial frame for spatial choices in another frame. Effective use of the stimuli after their rotation suggested that the monkeys perceived the stimuli as a representation of the configuration of the touch holes in the real space, not only as different geometrical patterns without configuration information.

• MeSH
• diskriminační učení fyziologie   MeSH
• hmat fyziologie   MeSH
• Macaca mulatta MeSH
• operantní podmiňování fyziologie   MeSH
• orientace fyziologie   MeSH
• reakční čas fyziologie   MeSH
• rotace MeSH
• rozpoznávání obrazu fyziologie   MeSH
• světelná stimulace metody   MeSH
• vnímání prostoru fyziologie   MeSH
• vnímání tvaru fyziologie   MeSH
• výběrové chování fyziologie   MeSH
• zraková percepce fyziologie   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Hippocampal place cells represent different environments with distinct neural activity patterns. Following an abrupt switch between two familiar configurations of visual cues defining two environments, the hippocampal neural activity pattern switches almost immediately to the corresponding representation. Surprisingly, during a transient period following the switch to the new environment, occasional fast transitions between the two activity patterns (flickering) were observed (Jezek, Henriksen, Treves, Moser, & Moser, ). Here we show that an attractor neural network model of place cells with connections endowed with short-term synaptic plasticity can account for this phenomenon. A memory trace of the recent history of network activity is maintained in the state of the synapses, allowing the network to temporarily reactivate the representation of the previous environment in the absence of the corresponding sensory cues. The model predicts that the number of flickering events depends on the amplitude of the ongoing theta rhythm and the distance between the current position of the animal and its position at the time of cue switching. We test these predictions with new analysis of experimental data. These results suggest a potential role of short-term synaptic plasticity in recruiting the activity of different cell assemblies and in shaping hippocampal activity of behaving animals.

• Klíčová slova
• CA3, attractor neural network, hippocampus, memory, place cell, recurrent neural network, teleportation, theta,
• MeSH
• akční potenciály fyziologie   MeSH
• časové faktory MeSH
• elektroencefalografie MeSH
• hipokampus cytologie   MeSH
• krysa rodu Rattus MeSH
• mapování mozku MeSH
• modely neurologické * MeSH
• nervová síť fyziologie   MeSH
• neurony fyziologie   MeSH
• neuroplasticita fyziologie   MeSH
• podněty MeSH
• prostorová paměť fyziologie   MeSH
• světelná stimulace MeSH
• theta rytmus EEG fyziologie   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu Rattus MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

In dynamic environments, a central task of the attentional system is to keep track of objects changing their spatial location over time. In some instances, it is sufficient to track only the spatial locations of moving objects (i.e., multiple object tracking; MOT). In other instances, however, it is also important to maintain distinct identities of moving objects (i.e., multiple identity tracking; MIT). Despite previous research, it is not clear whether MOT and MIT performance emerge from the same tracking mechanism. In the present report, we study gaze coherence (i.e., the extent to which participants repeat their gaze behaviour when tracking the same object locations twice) across repeated MOT and MIT trials. We observed more substantial gaze coherence in repeated MOT trials compared to the repeated MIT trials or mixed MOT-MIT trial pairs. A subsequent simulation study suggests that MOT is based more on a grouping mechanism than MIT, whereas MIT is based more on a target-jumping mechanism than MOT. It thus appears unlikely that MOT and MIT emerge from the same basic tracking mechanism.

• Klíčová slova
• Attention, Eye movements, Multiple identitty, Multiple object tracking, Tracking,
• MeSH
• korelace dat MeSH
• lidé MeSH
• mladý dospělý MeSH
• modely neurologické * MeSH
• oční fixace * fyziologie   MeSH
• pohyb těles MeSH
• pravděpodobnost MeSH
• reprodukovatelnost výsledků MeSH
• rozpoznávání obrazu * fyziologie   MeSH
• světelná stimulace MeSH
• vnímání pohybu * fyziologie   MeSH
• Check Tag
• lidé MeSH
• mladý dospělý MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• srovnávací studie MeSH

What is the neural substrate of our capability to properly react to changes in the environment? It can be hypothesized that the anterior cingulate cortex (ACC) manages repetitive stimuli in routine conditions and alerts the dorsolateral prefrontal cortex (PFC) when stimulation unexpectedly changes. To provide evidence in favor of this hypothesis, intracerebral stereoelectroencephalographic (SEEG) data were recorded from the anterior cingulate and dorsolateral PFC of eight epileptic patients in a standard visual oddball task during presurgical monitoring. Two types of stimuli (200 ms duration) such as the letters O (frequent stimuli; 80% of probability) and X (rare stimuli) were presented in random order, with an interstimulus interval between 2 and 5 s. Subjects had to mentally count the rare (target) stimuli and to press a button with their dominant hand as quickly and accurately as possible. EEG frequency bands of interest were theta (4-8 Hz), alpha (8-12 Hz), beta (14-30 Hz), and gamma (30-45 Hz). The directionality of the information flux within the EEG rhythms was indexed by a directed transfer function (DTF). The results showed that compared with the frequent stimuli, the target stimuli induced a statistically significant increase of DTF values from the anterior cingulate to the dorsolateral PFC at the theta rhythms (P < 0.01). These results provide support to the hypothesis that ACC directly or indirectly affects the oscillatory activity of dorsolateral PFC by a selective frequency code under typical oddball conditions.

• MeSH
• akční potenciály fyziologie   MeSH
• biologické hodiny fyziologie   MeSH
• cingulární gyrus anatomie a histologie   fyziologie   MeSH
• dospělí MeSH
• duševní procesy fyziologie   MeSH
• elektroencefalografie metody   MeSH
• evokované potenciály fyziologie   MeSH
• interpretace statistických dat MeSH
• kognice fyziologie   MeSH
• lidé MeSH
• mapování mozku MeSH
• mladý dospělý MeSH
• nervové dráhy anatomie a histologie   fyziologie   MeSH
• neurony fyziologie   MeSH
• neuropsychologické testy MeSH
• počítačové zpracování signálu MeSH
• prefrontální mozková kůra anatomie a histologie   fyziologie   MeSH
• světelná stimulace MeSH
• Check Tag
• dospělí MeSH
• lidé MeSH
• mladý dospělý MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The Greenland Ice Sheet harbours a wealth of microbial life, yet the total biomass stored or exported from its surface to downstream environments is unconstrained. Here, we quantify microbial abundance and cellular biomass flux within the near-surface weathering crust photic zone of the western sector of the ice sheet. Using groundwater techniques, we demonstrate that interstitial water flow is slow (~10-2 m d-1), while flow cytometry enumeration reveals this pathway delivers 5 × 108 cells m-2 d-1 to supraglacial streams, equivalent to a carbon flux up to 250 g km-2 d-1. We infer that cellular carbon accumulation in the weathering crust exceeds fluvial export, promoting biomass sequestration, enhanced carbon cycling, and biological albedo reduction. We estimate that up to 37 kg km-2 of cellular carbon is flushed from the weathering crust environment of the western Greenland Ice Sheet each summer, providing an appreciable flux to support heterotrophs and methanogenesis at the bed.

• MeSH
• biomasa * MeSH
• hydrologie MeSH
• koloběh uhlíku MeSH
• ledový příkrov chemie   mikrobiologie   MeSH
• počasí MeSH
• počet mikrobiálních kolonií MeSH
• uhlík analýza   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Grónsko MeSH
• Názvy látek
• uhlík MeSH

A total of 152 aerosol and spider web samples were collected: 96 spider's webs in karst areas in 4 European countries (Czech Republic, France, Italy, and Slovakia), specifically from the surface environment (n = 44), photic zones of caves (n = 26), and inside (aphotic zones) of caves (n = 26), 56 Particulate Matter (PM) samples from the Sloupsko-Sosuvsky Cave System (speleotherapy facility; n = 21) and from aerosol collected from the nearby city of Brno (n = 35) in the Czech Republic. Nontuberculous mycobacteria (NTM) were isolated from 13 (13.5%) spider's webs: 5 isolates of saprophytic NTM (Mycobacterium gordonae, M. kumamotonense, M. terrae, and M. terrae complex) and 6 isolates of potentially pathogenic NTM (M. avium ssp. hominissuis, M. fortuitum, M. intracellulare, M. peregrinum and M. triplex). NTM were not isolated from PM collected from cave with the speleotherapy facility although mycobacterial DNA was detected in 8 (14.3%) samples. Temperature (8.2 °C, range 8.0-8.4 °C) and relative humidity (94.7%, range 93.6-96.6%) of air in this cave were relatively constant. The average PM2.5 and PM10 mass concentration was 5.49 µg m-3 and 11.1 µg m-3. Analysed anions (i.e., F-, Cl-, NO2-, SO42-, PO43- and NO3-) originating largely from the burning of wood and coal for residential heating in nearby villages in the surrounding area. The air in the caves with speleotherapy facilities should be monitored with respect to NTM, PM and anions to ensure a safe environment.

• Klíčová slova
• asthma therapy, cave airflow, mycobacteria other than tuberculosis (MOTT), non-tuberculous mycobacteria (NTM), risk groups of microorganisms, saprophytic environmental mycobacteria, underground therapy,
• Publikační typ
• časopisecké články MeSH