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Adaptation of trigeminal ganglion cells to periodic whisker deflections.

Trigeminal ganglion neurons in adult rats adapt to periodic whisker deflections in the range of 1-40 Hz, manifested as a reduction in spike counts to progressively later stimuli in a train of pulsatile or sinusoidal deflections. For high velocity, pulsatile deflections, adaptation is time- and frequency-dependent; as in the case of thalamic and cortical neurons, adaptation is greater at higher stimulus frequencies. With slower velocity, sinusoidal movements, trigeminal ganglion cells differ from central neurons, however, by exhibiting strong adaptation even at low frequencies. For both types of stimuli, effects in trigeminal ganglion neurons were more pronounced in rats maintained during the recording session under neuromuscular blockade than in non-paralysed animals. Results are consistent with previous findings in other systems that frequency-dependent adaptation of cutaneous primary afferent neurons is affected by mechanical properties of the skin. Such effects are likely to vary depending on the nature of the whisker stimuli and physiological states that affect skin viscoelasticity.

Adaptation, Physiological↗

PubMed1966

Exchange diffusion effect and euryhalinity in teleosts.

The sea water (SW)-adapted euryhaline Platichthys flesus, and the marine Serranus exchange about 50% of their internal sodium with the external sodium per hour. This rate of exchange decreases with decreasing salinity of the adaptation medium. When the flounder is transferred from SW to FW an instantaneous 90% reduction of the Na and Cl outflux is observed. About 30 min later a second, progressive, reduction occurs. The outflux reductions appear to result from two types of regulatory mechanisms reducing gill permeability and preventing excessive salt loss. The first reduction corresponds to independent "Na- and Cl-free effects" as shown by transfers to artificial media containing either Na or Cl with an impermeant co-ion. The pattern of simultaneous rapid variations of Na influx and outflux for a range of salinity changes in flounder adapted to SW, 1/2 SW, or 1/4 SW has been studied. The data are compatible with the hypothesis of an exchange diffusion mechanism characterized by a coupling of both unidirectional fluxes. The affinity of the exchange diffusion carrier for sodium has been measured (Km approximately equal to 400 mM). The delayed reduction would result from a progressive diminution of the quantity of carrier available but without modification of its affinity for sodium. When the stenohaline marine perch is transferred from SW to FW, a 40% reduction of the outflux is observed. But it is not the result of an exchange diffusion effect as it is related to the external osmolarity change and not to the NaCl concentration change. Furthermore no delayed reduction is observed after transfer into FW. This transfer is accompanied by a heavy loss of electrolytes resulting in a rapid decline of the plasma electrolyte level and death. A comparative survey of the relative importance of these regulatory mechanisms has been made.

Adaptation, Physiological↗

PubMed1989

Replacement rate of free fatty acids in fasted rats adapted to a high-protein diet.

1. Free fatty acid (FFA) mobilization during fasting was measured in cats fed a meat diet (63% protein, 18% fat, 6% carbohydrate, w/w) or a carbohydrate-rich diet (15% protein, 10% fat, 70% carbohydrate), and in rats adapted to a high-protein, carbohydrate-free synthetic diet (70% casein, 8% fat) or a balanced synthetic diet (66% carbohydrate, 17% casein, 8% fat). 2. Fasted cats and rats on the high-protein diet showed reduced rates of plasma FFA increase. Their blood glucose was unchanged but higher than that of controls fed a carbohydrate-rich diet after fasting for 24 (rats) or 48 h (cats). 3. The steady-state rate of plasma FFA replacement was determined with 1-[14C]-palmitate in fed and fasted rats with plasma FFA levels ranging from 0.30 to 1.45 mumol/ml adapted to the high-protein or to the balanced diet. Under these dietary conditions, the FFA replacement rates were linearly related to the concentration of plasma FFA. However, the slope of the regression line was steeper for the rats on the high-protein diet. Thus, for the same concentration of plasma FFA, replacement rates for rats adapted to the high-protein diet were higher than for controls. 4. These data indicate that the higher rates of FFA replacement required in situations demanding an increased supply of FFA for animals on high-protein regimens are attained with smaller increases in plasma FFA concentration.

Animals↗

PubMed2000

Environmental press and adaptation to disability in hospitalized live-alone older adults.

PURPOSE: This study examined the ability of personal competency variables at the time of hospital discharge to predict primary instrumental activities of daily living (IADLs) and secondary outcomes (living arrangements) in a sample of 194 urban, live-alone, older adults who had a new onset disability. DESIGN AND METHODS: Consecutively admitted medical rehabilitation patients, 72% women and 85% African American, participated in the study. Using path analysis, three of the four competency variables collected at the time of hospitalization (cognition, medical burden, activities of daily living) predicted IADLs at 3 and 6 months after hospitalization (e.g., cooking, telephone use, money management). IADLs, in turn, predicted living arrangements at 3 and at 6 months after hospitalization. RESULTS: The findings provided strong support for the importance of assessing a broad range of competency variables when investigating adaptation to disability. IMPLICATIONS: The increased understanding of adaptation in live-alone older adults with a new-onset disability is particularly timely given the increase in live-alone older adults and the dire consequences associated with change in living arrangement (i.e., mortality and morbidity) in this group.

Activities of Daily Living↗

PubMed1989

Molecular basis of evolutionary adaptation at the lactate dehydrogenase-B locus in the fish Fundulus heteroclitus.

At the extremes of its natural distribution, populations of the common killifish Fundulus heteroclitus experience a difference of more than 15 degrees C in mean annual temperature. These populations are virtually fixed for two different codominant alleles at the heart-type lactate dehydrogenase locus (Ldh-B) which code for allozymes with different and adaptive kinetic responses to temperature. Two populations near the extremes of the species range (i.e., Maine and Georgia) were further studied for thermal adaptation at this locus. In the absence of any kinetic differences one would predict that to maintain a constant reaction velocity, 2 to 3 times as much enzyme would be required for each 10 degrees C decrease in environmental temperature. Consistent with this adaptive strategy and in addition to the adaptive kinetic characteristics, the LDH-B4 enzyme (EC 1.1.1.27) concentration and its mRNA concentration were approximately twice as great in the northern population as in the southern population. Acclimation experiments allow us to conclude that these differences are due to a combination of fixed genetic traits (evolutionary adaptation) and plastic responses to temperature (physiological acclimation). Furthermore, our calculations show that the LDH-B4 reaction velocities are essentially equivalent for these two populations, even though they live in significantly different thermal environments.

Adaptation, Physiological↗

PubMed1994

Adaptive plasticity of the auditory space map in the optic tectum of adult and baby barn owls in response to external ear modification.

1. This study demonstrates the influence of experience on the establishment and maintenance of the auditory map of space in the optic tectum of the barn owl. Auditory experience was altered either by preventing the structures of the external ears (the facial ruff and preaural flaps) from appearing in baby barn owls (baby ruff-cut owls) or by removing these structures in adults (adult ruff-cut owls). These structures shape the binaural cues used for localizing sounds in both the horizontal and vertical dimensions. 2. The acoustic effects of removing the external ear structures were measured using probe tube microphones placed in the ear canals. In both baby and adult ruff-cut owls, the spatial pattern of binaural localization cues was dramatically different from normal: interaural level difference (ILD) changed with azimuth instead of with elevation, the rate of change of ILD across space was decreased relative to normal, and the rate of change of interaural time difference (ITD) across frontal space was increased relative to normal. 3. The neurophysiological representations of ITD and ILD in the optic tectum were measured before and > or = 3 mo after ruff removal in adults and beginning at 4.5 months of age in baby ruff-cut owls. Multiunit tuning to ITD and to ILD was measured using dichotic stimulation in ketamine-anesthetized owls. The tectal maps of ITD and ILD were reconstructed using visual receptive field location as a marker for recording site location in the optic tectum. 4. Adjustment of the tectal map of ITD to the altered spatial pattern of acoustic ITD was essentially complete in adults as well as in baby ruff-cut owls. This adjustment changed the magnification of ITD across the tectum, with resultant changes in ITD tuning at individual tectal sites of up to approximately 25 microseconds (approximately 5% of the physiological range) relative to normal values. 5. Adaptation of the tectal ILD map to the ruff-cut spatial pattern of acoustic ILD was substantial but clearly incomplete in both adult and baby ruff-cut owls. Although changes of up to approximately 15 dB (approximately 47% of the physiological range) relative to normal tuning were observed at certain tectal sites, the topography of the ILD map was always intermediate between normal and that predicted by the ruff-cut spatial pattern of acoustic ILD.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1999

The importance of the feeding current for oxygen uptake in the water flea daphnia magna

In the planktonic crustacean Daphnia magna (Branchiopoda, Cladocera), different views exist on the mechanism of respiratory gas exchange, ranging from gill breathing to general integumentary respiration. The presumed structures for specialized gas exchange are located ventrally within the filter chamber, which is continuously perfused with the ambient medium for food gathering. To localize respiratory gas exchange in D. magna, we determined the contribution of the feeding current to total oxygen transport. Combining microscopy with special optical techniques, we used a phosphorescent oxygen-sensitive dye for oxygen partial pressure (PO2) measurements and applied fluorescent microspheres for flow-rate analysis. Appendage beat rate was determined by digital image-processing. All experiments were carried out on hypoxia-adapted animals with a body length ranging from 2.3 to 2.7 mm at 20 degreesC. External PO2 measurement revealed oxygen depletion in the ventral body region but essentially no change at posterior, lateral and dorsal positions. The PO2 difference between the inflow and outflow of the feeding current was 13.0 mmHg (1.73 kPa). The flow rate of the feeding current ranged from 1.2 to 5.2 ml h-1 and showed a close correlation with appendage beat rate, which varied from 310.4 to 460.7 beats min-1. Model calculations based on the Fick principle suggest that oxygen extraction from the feeding current satisfies most of the total of oxygen requirement of D. magna.

Journal Article↗

PubMed1989

[Response characteristics of fast-adapting units innervating cat oral mucosa to ramp-shaped pressure and triangular vibratory stimuli].

In this study, responses of fast-adapting sensory units to ramp-shaped pressure and triangular vibratory stimuli were recorded in the molar lingual gingiva and the alveolar mucosa isolated from the cat mandible via the air-gap method. The receptors of the fast-adapting units were classified into five types by a morphological study and the response characteristics of the individual sensory unit were investigated by electrophysiological methods. 1. Fast-adapting units of cat oral mucosa were found to have had five types of encapsulated endings (Type I-V) via a microscopical study. Among the 1,609 endings observed, the occurrence frequency of the individual receptor type was as follows: Type I 64.1%, Type II 9.5%, Type III 13.9%, Type IV 1.2% and Type V 11.3%. Although Type V a-d receptors had not been observed in the cat oral mucosa, their presence was demonstrated in whole thickness preparation stained with methylene blue. 2. The impulse frequency-displacement velocity curves (long-long coordinated) of 32 fast-adapting units (20 animals) showed four different patterns. 9.3% of the fast-adapting units showed a proportional relationship over all ranges of displacement velocity in the impulse frequency-displacement velocity relation. 25.0% showed a proportional relationship in an initial narrow range of displacement velocity and attained a steady state in the higher range. In 21.9% of these units, the impulse frequency remained steady over all the ranges. In the remaining 43.8%, the impulse frequency remained steady in singular range over all displacement velocities tested, however their response times decreased when the displacement velocity was increased. 3. The fast-adapting units were divided into two groups by response mode: a unit group with a Type I receptor and the other with Type II-V receptors (represented by a Type III receptor). The slopes were measured from their relations (log-log coordinates) in threshold amplitude vs. displacement caused by single triangular stimulus. The slope for the Type I group was -0.796 +/- 0.099 (mean +/- S. D.) (Range: -0.593(-)-1.017, n = 22). The slope for the other group was -0.658 +/- 0.024 (Range: -0.607(-)-0.758, n = 6). The slope of the former was larger than that of the latter. 4. The threshold-frequency curves (tuning curve; semilog coordinates) for the Type I group and the other group were analyzed. Both tuning curves of these sensory units revealed no plateaus between the lower-frequency limits and the upper-frequency limits.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2005

[The LISA trial-a- randomized, double-blind, placebo-controlled four-arm study of 1,000 patients with nodular goiter in Germany. Study Design and first results of feasibility].

BACKGROUND: Although levothyroxine is the mostly prescribed medicament in Germany, its therapeutic effectiveness in nodular goiter was never studied in a randomized, double-blind trial with sufficient power. Thus, in May 2004 a TSH-adapted (TSH: thyroid-stimulating hormone), randomized, doubleblind, placebo-controlled four-arm (placebo [P] vs. levothyroxine [T] vs. iodine [I] vs. levothyroxine + iodine [TI]) multicenter study was started in Germany (LISA study). PATIENTS AND METHODS: Based on former retrospective and prospective studies, it was calculated that a sufficient statistical power (> 80%) would be achieved with 250 patients in each arm. The primary endpoint of the trial is the 1-year change of ultrasonographically measured total volume of all nodules. Secondary criteria are volume of goiter, number of nodules, and echogenic structure of nodules. While the study is kept strictly double-blind, the dose of levothyroxine in the T and TI groups is adapted once according to 3-month TSH measurements (target range 0.2-0.8 mU/l). RESULTS: Up to now (1 year after beginning), 305 patients have been included. TSH adaptation could be performed without compromising the double-blind character of the study with good results: about 90% of the patients reached the TSH target range. CONCLUSION: Unblinded results are to be expected in 2007.

Adolescent↗

PubMed1993

The effect of position of immobilisation on resting length, resting stiffness, and weight of the soleus muscle of the rabbit.

The extent of immobilisation-induced adaptations of muscle length and muscle weight is known to be profoundly influenced by the position (or length) at which the muscle is immobilised. However, the effect of the full range of positions of immobilisation on subsequent adaptations of muscle length and weight has not yet been investigated. To examine further the effect of position of immobilisation, we used cast-immobilisation of the hind limbs of 23 rabbits, in various positions between full plantar flexion and full dorsiflexion. Six muscles from non-immobilised rabbits were used as the controls. After 10 days of immobilisation, the wet weight of the soleus muscle and the resting length and resting stiffness of the soleus muscle-tendon unit were determined. Immobilisation in a shortened position was associated with a significantly greater decrease in length and weight than was immobilisation in a lengthened position. In addition, immobilisation produced significant increases in the resting stiffness of muscle-tendon units, although there was no evidence of a position-dependent increase in stiffness. Muscle weight was influenced by the position of immobilisation in a nonlinear way. The data support the views that the pre-immobilisation resting length of the muscle represents a threshold length and that immobilisation at lengths longer than this retards immobilisation-induced atrophy.

Animals↗

PubMed2006

Inactivation of ppk differentially affects virulence and disrupts ATP homeostasis in Salmonella enterica serovars Typhimurium and Gallinarum.

Polyphosphate is involved in resistance to stress in a number of bacterial species; however, its role in the virulence of Salmonella enterica serovars which differ in their host range has not been described. We examined the role of polyphosphate kinase in infection, growth and survival of S. Typhimurium (broad-host range) and S. Gallinarum (avian-adapted). We also used ppk mutants to assess the downstream effects on intracellular ATP levels. ppk mutants had significantly (P<0.05) elevated ATP in stationary phase compared to the wild-type and, depending on the serovar, were defective in growth, survival and virulence. The virulence of S. Typhimurium ppk::SpcStr was significantly (P<0.05) attenuated following oral infection of both Rhode Island Red chickens and BALB/c mice. In contrast, inactivation of the ppk gene of S. Gallinarum did not affect growth or virulence. The differential contribution of polyphosphate to the virulence of S. Typhimurium and S. Gallinarum may reflect aspects of the pathogenesis and host range of these serovars. The ppk mutant of both serovars survived significantly less well (P<0.05) in a saline starvation-survival model, relative to the respective parent. The effect of ppk mutation on survival was formally described by fitting the data to the Weibull model and by estimation of k(max). Measurement of rpoS promoter activity using a lacZ transcriptional fusion demonstrated repression of rpoS in a ppk background, confirming a role for polyphosphate in RpoS induction. Together the data indicate the crucial importance of maintaining stable intracellular ATP during infection and nutritional stress. We suggest that polyphosphate plays a central role in homeostasis during growth and stress.

Adenosine Triphosphate↗

PubMed2006

Retention of adaptive control over varying intervals: prevention of slip- induced backward balance loss during gait.

Stability improvements made in a single acquisition session with merely five slips in walking are sufficient to prevent backward balance loss (BLOB) at the end of session, but not after 12 mo. The purpose of this study was to determine whether the effect of an enhanced single acquisition session would be retainable if tested sooner, at intervals of < or =4 mo. Twenty-four young subjects were exposed to blocks of slip, nonslip, and both types of trials during walking at their preferred speed in the acquisition session. In each of the four follow-up sessions around 1 wk, 2 wk, 1 mo, and 4 mo later, these same subjects experienced only a single slip after eight to 13 unperturbed walking trials in an otherwise identical setup. Gait stability was obtained as the shortest distance between the measured center of mass (COM) state (position and velocity) and the mathematically predicted threshold for BLOB at pre- and postslip, corresponding to the instants of touchdown of the slipping limb and liftoff of the contralateral limb, respectively. During the acquisition session, pre- and postslip stability improved significantly, resulting in a reduction of BLOB from 100% in the first slip (S1) to 0% in the last slip (S24), with improvements converging to a steady state, that enabled all of the subjects to avoid BLOB, regardless of whether a slip occurred. During retest sessions, subjects' preslip stability was not different from that in S24, but was greater than that in S1. Their postslip stability was also greater than that in S1 but less than that in S24, resulting in BLOB at a 40% level. No difference was found in any of these aspects between each follow-up session. These adaptive changes were associated with a range of individual differences, varying from no detectable deterioration in all aspects (n = 8) to a consistent BLOB in all follow-ups (n = 3). Our findings demonstrated the extent of plasticity of the CNS, characterized by rapid acquisition of a stable COM state under unpredictable slip conditions and retention of such improvements for months, resulting in a reduced occurrence of unintended backward falling.

Adaptation, Physiological↗

PubMed2006

Larval tolerance, gene flow, and the northern geographic range limit of fiddler crabs.

Despite growing interest in species' range shifts, little is known about the ecological and evolutionary factors that control geographic range boundaries. We investigated the processes that maintain the northern range limit of the mud fiddler crab (Uca pugnax) at North Scituate, Massachusetts, USA (42 degrees 14' N), located approximately 60 km north of Cape Cod. Larvae from five populations in Massachusetts were reared under controlled temperatures to test whether cooler water near the edge of this species' range inhibits planktonic development. Few larvae completed development at temperatures < 18 degrees C, a threshold that larvae would regularly encounter north of Cape Cod. Extensive salt marshes are present north of the current range boundary, and a transplant experiment using field enclosures confirmed that benthic fiddler crabs can survive severe winter conditions in this northern habitat. Taken with oceanographic data, these results suggest that the range boundary of fiddler crabs is likely maintained by the influence of cooler water temperatures on the larval phase. Analyses of mitochondrial DNA sequences from a neutral marker (COI) indicate high gene flow among U. pugnax populations in Massachusetts with little differentiation across Cape Cod. Consistent with predictions regarding the homogenizing influence of gene flow, larvae from source populations north and south of Cape Cod shared a common lower threshold for development. However, larvae produced near the range edge had faster growth rates than those from the south side of Cape Cod (typically reaching the final megalopal stage 1.0-5.5 d faster at 18 degrees C). Additional studies are needed to determine the mechanism underlying this counter-gradient variation in development time. We hypothesize that dispersal into cooler water on the north side of Cape Cod may act as a selection filter that sieves out slow developers from the larval pool by increasing planktonic duration and exposure to associated sources of mortality. Thus while high gene flow may prevent the evolution of greater cold tolerance in northern populations, recurrent selection on existing variation may lead to an unexpected concentration of favorable adaptations at the edge of the range. Such a pattern could permit edge populations to play a dominant and unrecognized role in future range extensions.

Animals↗

PubMed2003

Control strategy for maintaining physiological perfusion with rotary blood pumps.

We present arguments and simulation results in favor of a novel strategy for control of rotary blood pumps. We suggest that physiological perfusion is achieved when the blood pump is controlled to maintain an average reference differential pressure. In the case of rotary left ventricular assist devices, our simulations show that maintaining a constant average pressure difference between the left ventricle and aorta results in physiological perfusion over a wide range of physical activities and clinical cardiac conditions. We simulated rest, light, and strenuous exercise conditions, corresponding to cardiac demands of 4.92, 7.98, and 14.62 L/min, respectively. For different exercise levels, the clinical conditions ranged from normal to failing to asystolic heart. By maintaining a constant pressure difference of 75 mm Hg between the left ventricle and aorta, with either an axial or a centrifugal blood pump, a total cardiac output close to the physiological cardiac demand was achieved, irrespective of the heart condition. The simulations of the transitions between different levels of exercise indicate that with the same reference differential pressure, the proposed approach leads to rapid adaptation of the total cardiac output to physiological levels, while avoiding suction. Comparison with the traditional control strategy of maintaining a reference rotational speed (rpm) of the pump indicates that though the traditional approach has some degree of adaptability, it is only adequate over a narrow range of cardiac demand and clinical conditions of the patient. Our results indicate that the proposed approach is superior to the alternatives in providing an adequate and autonomous adaptation of the total cardiac output over a broad range of exercise conditions (expected when an assist device is used as a destination therapy) and clinical statuses of the native heart (such as further deterioration or recovery of cardiac function), while having the potential to improve the quality of life of patients by reducing the need for monitoring and frequent human intervention. The proposed approach can be clinically implemented using simple controllers, and requires the implantation of two pressure sensors, or estimation of the pressure difference based on other available measurements.

Biomechanical Phenomena↗

PubMed1988

Principles of flow cytometry.

Flow cytometers can analyze a populations of cells, one at a time, at rates of 1,000 to 10,000 cells per second. They can provide distributions of parameters, not just the MCV. A broad variety of measurement parameters is available, ranging from simple sizing to esoteric measures of membrane fluidity or epitope density. The resulting analysis gives low resolution compared to imaging of cells but gives excellent statistical samples of the parameters that it can detect. The parameter values for individual cells can be correlated, and displayed in a variety of multi-dimensional formats. When the analysis reveals subsets of cells, it is possible to sort the detected subsets of cells into separate chambers for further culture or test. Flow cytometers are already in clinical laboratories, performing size analysis in multiparameter hematology instruments. As you have seen, this usage barely scratches the surface of the capabilities of this technology. It now remains for the research clinician to adapt flow cytometry to a broader range of useful clinical applications.

Calibration↗

PubMed2005

Introducing assistive technology into the existing homes of older people: feasibility, acceptability, costs and outcomes.

We examined how far, and at what cost, the housing stock could be modified to accommodate the assistive technology (AT) necessary to enable older people to remain in their own homes. A multidisciplinary team devised seven hypothetical user profiles for 10 case study areas, with five local authorities and five housing associations in England and Wales. Each profile was considered at two times, five years apart, with the users' functional abilities deteriorating in between. In addition, in-depth interviews were carried out with a sample of 67 older people in the case study areas about their use and experience of a wide range of AT. The interviews showed the need to listen to older people and that they welcomed AT when it addressed a perceived need. The results showed that the extent of adaptation required of buildings to accommodate a user's needs varied greatly. It was also found that there was confusion about the terminology of AT, including the idea of the 'smart house'. The study shows that the adaptability of the housing depends on a range of factors and costs.

Activities of Daily Living↗

PubMed1995

Cholinergic modulation of cortical oscillatory dynamics.

1. The effect of cholinergic modulation on cortical oscillatory dynamics was studied in a computational model of the piriform (olfactory) cortex. The model included the cholinergic suppression of neuronal adaptation, the cholinergic suppression of intrinsic fiber synaptic transmission, the cholinergic enhancement of interneuron activity, and the cholinergic suppression of inhibitory synaptic transmission. 2. Electroencephalographic (EEG) recordings and field potential recordings from the piriform cortex were modeled with a simplified network in which cortical pyramidal cells were represented by excitatory input/output functions with gain parameters dependent on previous activity. The model incorporated distributed excitatory afferent input and excitatory connections between units. In addition, the model contained two sets of inhibitory units mediating inhibition with different time constants and different reversal potentials. This model can match effectively the patterns of cortical EEG and field potentials, showing oscillatory dynamics in both the gamma (30-80 Hz) and theta (3-10 Hz) frequency range. 3. Cholinergic suppression of neuronal adaptation was modeled by reducing the change in gain associated with previous activity. This caused an increased number of oscillations within the network in response to shock stimulation of the lateral olfactory tract, effectively replicating the effect of carbachol on the field potential response in physiological experiments. 4. Cholinergic suppression of intrinsic excitatory synaptic transmission decreased the prominence of gamma oscillations within the network, allowing theta oscillations to predominate. Coupled with the cholinergic suppression of neuronal adaptation, this caused the network to shift from a nonoscillatory state into an oscillatory state of predominant theta oscillations. This replicates the longer term effect of carbachol in experimental preparations on the EEG potential recorded from the cortex in vivo and from brain-slice preparations of the hippocampus in vitro. Analysis of the model suggests that these oscillations depend upon the time constant of neuronal adaptation rather than the time constant of inhibition or the activity of bursting neurons. 5. Cholinergic modulation may be involved in switching the dynamics of this cortical region between those appropriate for learning and those appropriate for recall. During recall, the spread of activity along intrinsic excitatory connections allows associative memory function, whereas neuronal adaptation prevents the spread of activity between different patterns. During learning, the recall of previously stored patterns is prevented by suppression of intrinsic excitatory connections, whereas the response to the new patterns is enhanced by suppression of neuronal adaptation.

Adaptation, Physiological↗

PubMed1976

The neuronal basis of a sensory analyser, the acridid movement detector system. I. Effects of simple incremental and decremental stimuli in light and dark adapted animals.

1. The response of the movement detector (MD) system to proportionally constant incremental and decremental stimuli has been studied at various degrees of light and dark adaptation. Action potentials in the descending contralateral movement detector neurone were taken as the indicator of response. 2. Over a range of at least six log10 units of adapting luminance, the MD system behaves as an ON/OFF unit, giving responses to both incremental and decremental changes in the illumination of a 5 degrees target. 3. With increasing amplitudes of stimuli, both the ON and OFF responses saturate rapidly. Saturation is reached sooner at higher levels of light adaptation. At all levels of light adaptation, the OFF response is greater than the ON. The ratio for saturating stimuli is approximately constant at around 3:2. 4. At the brightest adapting luminances used (20 000 cd/m2) the ON response is reduced but not lost. At the lowest (0-004 cd/m2) the OFF response to a 5 degrees disc fails, but can be regained by increasing the test area to 10 degrees. 5. From what is known of the retina of locusts and other insects, it is thought that light and dark adaptation in the MD system can be adequately explained by events at the retinula cell.

Action Potentials↗