Infant Primate Research Laboratory
The IPRL provides a wide range of intellectual and scientific services to investigators, including basic consultation, methodological design, sample size determination, selection of appropriate neurobehavioral measures, and data summary and interpretation to CHDD Research Affiliates studying non-human primates. The emphasis is on training affiliates and their staff on a wide range of behavioral tests to address hypotheses of interest.
Consulting services provide scientific, management, and budgetary information to affiliates as they develop new proposals. Advice and counsel on appropriate experimental designs, methods, and statistical approaches are provided to affiliates who are unfamiliar with the unique characteristics of developmental research using primates. Consultations regarding project management and resources are also provided during project development and implementation. Assistance is also provided for completing the required Animal Care and Use paperwork as well as forms required by the Primate Center and CHDD. Sharing of personnel, supplies, and equipment is typically arranged to reduce the cost of projects.
The IPRL is located in the Medical Research Tower and is supported by both the Center on Human Development and Disability (CHDD) and the Washington National Primate Research Center (WaNPRC).
Behavioral Testing Capabilities
The current testing battery includes the following assessments:
A Newborn Health Assessment modeled after the APGAR rating scale used with human infants is performed immediately after birth and again at approximately one-half hour after birth. Heart rate, respiration, rectal temperature, muscle tone, activity, and skin color are evaluated. As part of the Newborn Health Assessment, a systematic physical examination is performed to detect major birth defects. To this end, a physical examination of general appearance, skin, head, face, trunk, genitalia, and extremities is made.
Neonatal Behavioral Assessment Scale
A behavioral assessment procedure modeled after the Brazelton Neonatal Behavioral Assessment Scale is used to evaluate newborn reflexes and reactivity. The assessment begins with an observation of the infant’s state prior to testing and the position of the limbs in a resting position. The tester then removes the infant from its cage and wraps the infant in a diaper with the limbs exposed. The grasping response of the hands and feet are evaluated by placing the index finger against the palm of the hands and soles of the feet. Resistance of the arms and legs to extension is evaluated by gently pulling the limbs away from the body. The infant is then touched on the edge of the mouth and on the nose to elicit the rooting and snout response. To evaluate the startle response, a metal lid is dropped onto a counter in back of the infant. Next, the infant is turned away from the tester and the tester makes a lip smacking noise at the back of each ear to elicit an orienting response. A small plastic toy is then held in front of the infant and moved from side to side (on a horizontal plane) to examine visual orientation and visual following. The infant is then held above the counter and moved quickly in the direction of the counter to elicit the reflexive placing response of the feet and hands. To elicit a grasping response, the infant’s arms and legs are placed around the underside of a rolled-up cloth diaper and given the opportunity to grasp the diaper. Finally, the infant is placed in a supine position to elicit the righting response. After the infant is returned to its home cage, the tester evaluates the overall behavior state of the infant during testing and provides an evaluation of the overall irritability and consolability of the infant. Neonatal assessments take place every other day during the first 3 weeks of life.
Data from a five point scale to assess sleep-wakefulness and vital signs, i.e., respiration, heart rate and temperature are collected every four hours, 7 days/week to determine when these parameters begin to show evidence of diurnal cyclicity.
Intakes and Physical Growth Measurements
Animals are fed according to a pre-set protocol. Feedings begin within a few hours after birth with 10% dextrose in a water solution. Dextrose is continued every two hours for 4 to 5 feedings. A 50 human milk formula at 50% dilution is then provided every 2 hours for four days. After 4 days of age, feedings occur every 4 hours with full strength formula. Animals are typically self-feeding by 9 days of age. A slow weaning process begins at 91 days of age and animals are typically weaned off formula by approximately 120 days of age.
Physical growth is assessed by collecting measurements of crown-rump length, head size and foot size and monitoring the eruption of deciduous teeth. Crown-rump length is determined by placing the infant in a supine position on a metal sliding scale with the rump against the base of the scale and the crown of the head against a sliding barrier. The distance between the top of the infant's head and the rump is measured. Head circumference is determined with a measuring tape that is placed around the infant's head below the brow ridge, along the nuchal crest and above the ears, covering the occiput. Head width and length are determined using spreading calipers. Head width is measured using landmarks (just above and in front of the ears) that provide a measure of the two widest points of the skull. Head length is measured using the length from the area between the eyes to the occiput. Foot size is determined by placing the infant’s left foot on a metal sliding scale with the heel against the base of the scale and the toes against a sliding barrier. The distance between the infant's heel and the longest toe is measured. All anthropometric measures are recorded in mm. Animals are measured every 2 weeks until 2 months of age and then every month from 2 through 8 months of age. Physical measurements are taken at bimonthly intervals after 8 months from the area between the eyes to the occiput. Foot size is determined by placing the infant’s left foot on a metal sliding scale with the heel against the base of the scale and the toes against a sliding barrier. The distance between the infant's heel and the longest toe is measured. All anthropometric measures are recorded in mm. Animals are measured every 2 weeks until 2 months of age and then every month from 2 through 8 months of age. Physical measurements are taken at bimonthly intervals after 8 months. Infants are also examined for the eruption of deciduous teeth. Teeth are inspected on a daily basis until the central and lateral incisors and canines have erupted. After that, observations take place on a weekly basis until the first baby molar erupts. Once the first molar has erupted, observations are made daily until the remaining baby molars have all erupted.
Weights and Temperament
The collection of bodyweight data begins on the first day of life and continues until 10 months of age. Infants are removed from their home cage, placed in a carrier and transported to the weighing station. Weights are determined by placing the infant on a platform scale with digital readout. The scale is set to zero with the carrier and the weight is read and recorded. After the weight has been recorded, the animal is transported back to the home cage. During the weighing of the infant, aspects of early temperament (e.g., sociability, consolability, attention to environment) are scored by testers. Once a week, weight data are collected using a “novel probe” procedure. Briefly, the tester dresses in bright, unusual clothing and the temperament assessment is conducted as described above with the only change being the tester’s appearance. This allows the collection of temperament data under more challenging conditions.
Offspring Medical Treatment
Offspring are observed for signs of illness by trained veterinary technologists seven days/week. Clinical observations focus on detecting signs of dehydration, diarrhea, vomiting and lethargy. If signs of illness are observed, an appropriate medical treatment is initiated. All medical treatments are recorded on a form by the veterinary staff. Treatments are then coded with the daily weight data for each infant. The number of days that each infant is medicated can then be summarized across specific testing periods to assess the relationship between performance and the amount of medication received.
Object Retrieval Assessment
Infants are tested on an Object Retrieval Assessment to evaluate early sensorimotor development. Infants are provided an opportunity to reach for and retrieve an object that has been dipped in applesauce. Small brightly-colored plastic toys with rubber nipples attached to one end are used as stimuli. On each trial, infants are comfortably swaddled in cloth diapers and held by one examiner while a second examiner begins trials by dipping the nipple end of the object in the applesauce and allowing the infant to briefly suck on the nipple. The infant is then given a 15 sec. period to visually orient to the object as it is placed, within reach, on a horizontal test platform. Once the infant has oriented to the object, a 15 sec. period is provided to allow the infant to physically retrieve the object. The Object Retrieval Assessment begins at 2 weeks of age and infants are tested 4 days/week using 5 trials/day until they reach criterion.
Object Permanence Assessment
The development of object permanence is assessed according to procedures described for human infants by Jean Piaget and adapted for monkeys by Dr. Burbacher and his colleagues. A series of no hiding, partial hiding, and full hiding tasks are presented using a screen (2 days/ week) or a well (2 days/week) to hide the object. The hiding tasks consist of a 15 sec. orientation period and a 15 sec. response period. During the response period, however, the object is placed in front of the infant and is either: 1) not hidden from view, 2) partially hidden from view, or 3) fully hidden from view. All hidings take place while the infant is visually orienting to the object. Object Permanence Testing begins once infants reach criterion on the Object Retrieval Test. Fifteen trials, 5 of each hiding condition, are presented in random order during each session and test sessions take place 4 days/week. The A not B test commences after successful mastery of the full hiding trials on the screen and well test. For the A not B test, a series of full hiding trials is presented using a 2-well presentation board. After the infant retrieves the object from the wells on 2 consecutive trials (both trials use the same well, either RR or LL), the object is hidden in the opposite well in full view of the infant. Infants are required to grasp and retrieve the object from the well for a trial to be considered correct. Five trials are presented each day, 5 days/week until criterion is reached.
Motor Milestones and Social Behavior
Beginning at 20 days of age, infants are placed in a playroom for daily socialization with other infants (5 days/week). The playroom is equipped with shelves, a ramp, toys and a two-way observation window. Four separate shelves are located 19 to 38 in. above the playroom floor with an inclined wire mesh ramp attached to one of the shelves. Social behavior in mixed-sex play groups is coded in real time by a trained observer 2 days/week. Motor milestone data are also collected by observing when infants successfully climb up and down the ramp and climb or jump on and off the 4 separate shelves. Social data are collected until 10 months of age. After 10 months, animals continue to be socialized in the playroom or in gang cages but data on social behavior are not routinely collected.
Visual Acuity Assessment
A forced-choice preferential looking technique adapted from human infancy research is used to measure the development of spatial vision. The preferential looking technique relies on the strong visual preference for patterned surfaces over a gray field that is demonstrated by both human and nonhuman primate infants. Acuity is determined by showing infants various computer-generated black and white gratings (stripes) paired with a gray field of equal intensity. The tester observes the visual orientation responses of the infant (e.g., eye-widening, optokinetic nystagmus) and guesses the location (left or right) of the stripes. If the infant is able to see the stripes, the observer will be able to determine the location of the stripes above chance (> 75%). By varying the thickness of the stripes (i.e., varying the spatial frequencies), stimuli related to visual acuity from 0.5 to 28 cycles/degree (20/1400 to 20/23 Snellen) can be used to document the development of visual acuity. This procedure can be used as an early screening measure or to collect data on full function grating acuity. Infants from birth to 3 months of age can be tested using this procedure.
Visual Recognition Memory Assessment
The visual recognition memory test is based on the familiarization-novelty paradigm used extensively in human infancy research. This test paradigm makes use of the infant's proclivity to direct more visual attention to novel rather than previously seen (familiar) stimuli. Recognition memory is inferred from performance on the novelty paradigm, as some aspects of the familiar stimulus must be encoded in memory for the novelty response to occur. All stimuli are computer generated images presented on a large monitor. For each problem, the monkey is held by the investigator (swaddled in a diaper) and is presented with 2 identical patterns or faces during a familiarization period. Looking time to the left and right stimulus is recorded until a predetermined amount of total looking time is reached. After familiarization has been achieved, the infant is given an immediate two-part test trial, in which the stimulus used during the familiarization period is paired with a new (or novel) stimulus. Infants are tested on this procedure from 190 to 220 days postconception.
WGTA Tests of Learning and Memory
The Wisconsin General Test Apparatus (WGTA) has a long history of use in nonhuman primate research on learning and memory. For the WGTA tests, the monkey is placed in a testing cage equipped with a sliding opaque door that can be raised and lowered to allow access to a presentation board located in front of the cage. The presentation board has two shallow wells, one on the right and one on the left. The tester, sitting behind a screen that has been lowered places a food reward (grape or apple bit) in one of the wells on the presentation board and then covers the wells with test stimuli (3-dimensional junk objects/toys). The tester then raises the door to allow the monkey access to the presentation board. The monkey is given a certain amount of time to displace one of the test stimuli and, if correct, to obtain the fruit reward that was hidden in the well.
Once a response has been made, the sliding opaque door is lowered, the response is scored as correct or incorrect, and the next trial is set up. Infants start on this series of learning tests at 4 months and continue through 10 months. The IPRL current WGTA test battery includes the three tests listed below.
- Black-White Discrimination and Reversal: For this test, animals are required to associate a color (black or white block) with a fruit reward. When animals learn this association, the opposite color is rewarded requiring them to reverse their strategy. Animals receive 25 trials per day, five days per week, until a set criterion for correct responses is met.
- Hamilton Search: There are three stages to the Hamilton Search Test. In the first stage “Set Making,” the animals develop a search strategy to locate a food reward placed randomly in 1 of 4 boxes with lids. Animals are required to lift the lid on the box to obtain the reward. A perfect search strategy for this test is to open each box once and only once, until retrieving the reward. Animals receive 25 trials per day for five consecutive days. In the second stage, “Set Breaking,” the box that was least preferred in stage one is now baited on every trial, and the animal is allowed to open as many boxes as necessary in order to locate the reward. The order of the boxes does not change across trials within a test session. A perfect strategy would be to quickly discern that the same box location is now always rewarded and to only open that box on every trial. The third stage, “Forced Set Breaking,” is identical to stage two, with the exception that only one box opening is allowed on every trial.
- Two-choice Object Discrimination (Learning Set): For this test, animals are required to develop a win-stay, 10s shift strategy to solve the test problems. Animals are presented with 2 three-dimensional "junk" objects, one of which is rewarded for six consecutive trials. On the first presentation of a pair, a 50% chance of success is possible. After the first presentation, animals have sufficient information to perform at 100% correct on subsequent trials, since the same object is rewarded on all 6 trials. As the animal develops a win-stay, loss-shift strategy after the first trial, the percent of correct responses on trials 2-6 should increase. Thus, incremental increases in performance are typically observed on presentations 2-6. Six pairs of objects are run per day, five days per week. A total of 240 pairs are included in the test over an 8-week period.
Computer Learning System
Computer-based testing utilizing touch screens or joysticks has gained prominence with neurophysiologic studies of cognition as well as with purely behavioral studies involving human and nonhuman primates. The testing system developed at the IPRL makes use of touch screen technology to assess learning and memory. This system can assess learning and memory in infant macaques as young as 90-days of age, a methodology never before achieved with infant monkeys. Testing is conducted in a cage identical to the animal’s home-cage, with the exception that the back wall of the cage is a touch screen monitor. The monitor displays a template with square-shaped openings that line up with the response fields on the computer screen. A stainless steel tube enters through the bottom of the cage, with the end centered in front of the template. Liquid or semi-liquid rewards such as juice or applesauce are dispensed through this tube via a computer-controlled pneumatic pump system. Stimuli currently utilized include simple block patterns, digital images available on the World Wide Web, and digital images of the 3-dimensional "junk" objects that are used in WGTA testing. During training, animals are rewarded for simply touching one of the images on the touch sensitive screen.
After training, the animal proceeds through four cognitive tests that emulate tasks in the IPRL standard WGTA battery (Discrimination Learning, and Reversal, Spatial Search, Learning Set). Parameters that are specific to each task may be varied including, but not limited to, number of trials in a session, number of stimuli in the task, delays employed in the task, and type of stimuli presented on the task. New perceptual and cognitive tasks can also be developed that go beyond the abilities measured in WGTA including concepts related to facial processing, numerosity, spatial memory, metacognition, and categorical understanding. In addition to the standard WGTA tests listed above, the following tests have been developed for the computer learning apparatus: Delayed Response, Nonmatch-to-Sample, Nonmatch-to-Sample List Length, Match-to-Sample, and Match-to-Sample List Length.
To Use Our Services
Investigators who are interested in using infant primates in their projects are invited to
- Read about the equipment and services
- Contact either Thomas Burbacher at firstname.lastname@example.org, 206-685-7674 or Kimberly Grant at email@example.com, 206 685-1862.
To view Mouse Behavior Laboratory (MBL) click here
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