Postnatal Development of

Behavior

Unique Problems Facedby Altricial Neonates

1. Sensory immaturitystimuli available to adults not available toneonate

2. Motor immaturityability to act on motivations is limited

3. Physiological immaturitymotivational systems, regulatory systems

4. Morphological immaturitysmall size

Difficulties in AssessingBehavioral Development

Identification of eliciting stimuli

Motivations different from those of adults

Response definition(recall “isolation distress” of infant rats)

Mechanisms ofBehavioral Maturation

Integration and individuation

Threshold changes

CNS maturation

Response competition

Morphological change

Permissive/supportive environment

PermissiveEnvironment

CNS maturation (also indevelopment of locomotionin the frog)

How do we know if hiccuping and breathing are the samebehavior that differ only quantitatively, or whether they arequalitatively different behaviors? Should function matter? Should neural substrates matter? (Recall suckling and feeding, non-shivering thermgenesis; Response Definition)

McGraw, M. (1939) Swimming behavior of the human infant. J. Pediatrics, 15, 485-490.Is swimming at one year the same behavior as it is in the first few weeks?

First few weeks

Four months to one year

After approximately one year

Mechanisms ofBehavioral Maturation

Integration and individuation

Threshold changes

CNS maturation

Response competition

Morphological change

Permissive/supportive environment

McGraw, M. (1939) Swimming behavior of the human infant. J. Pediatrics, 15, 485-490.

First few weeks

Four months to one year

After approximately one year

Encephalization and the maturation of behaviorBritish neurologist John Hughlings Jackson“Doctrine of dissolution”

RhombencephalonThalamus

Hypothalamus

Prosencephalon

a. Nissl stain (cell bodies)

b. Weil stain (myelin)

Subthalamic nucleusFIG. 1. Parasagittal section through the brain of kitten K-l, showing the level and extent of transection. The rostra1 tilt of the cut is the result of growth of the brain in that direction in the weeks after the transection. Weil stain.

HistologyMesencephalon

Kitten #1

Kitten #3

Kitten #2

Histology

Behavior of Decerebrate KittensSuckling abolishedDecerebrate rigidity not observed

Reflexive eating and lapping of milk emerged at normal age of weaningTemperature regulation was only slightly impaired

All of the following developed in normal chronological orderauditory reflexes (orienting, pawing at source of sound)tactile placing reactions defensive reactions (piloerecton, hissing, bared teeth, biting)groomingpostural reflexes

Sleep-wake states developed normallyVisual recognition and social behavior were absentSome behaviors, e.g. pounce, “kill” behaviors, developed precociously, were exaggerated in form (hypermetria) and directed toward inappropriate stimuliThere were bouts of uncontrolled locomotion (hyperkinesis), with kittens sometimes

running pell-mell off table-topsAlso, “compulsive” climbing was observed.

McGraw, M. (1939) Swimming behavior of the human infant. J. Pediatrics, 15, 485-490.

First few weeks

Four months to one year

After approximately one year

Zelazo, P.R.,Zelazo, N.A. &Kolb, S. (1972)“Walking in thenewborn infant.Science, 176,314-315.

The first supporting evidence is the likelihood that newborn stepping does not ‘disappear”, but that stepping in the upright posture is masked by other developmental changes in the infant. First, in infants who no longer step, a simple alteration of posture -- that of placing infants supine — releases pattern generation identical to that of steps. Thelen and Fisher have suggested that biomechanical factors, rather than changes in central-neurological organization, account for this paradoxical result. Specifically, they suggested that the rapid acquisition of s.c. fat in the first 2 or 3 months of life taxed the available muscle strength when infants were in the demanding upright posture. When infants were placed supine, movements were facilitated. Indeed, infants who gained weight most rapidly between 2 and 6 weeks showed the most rapid decline in step rate. When growth changes were simulated by adding small weights to the legs of 1-month-old infants, their step rate and amplitude declined. Likewise, placing infants in torso-high water restored high levels of stepping, even in 3-month-old infants. These results suggest that when the context was appropriate, the underlying coordination traditionally believed to be cortically inhibited would become manifest.

Thelen, E. & Bradley, N. (1988) Motor development: Posture and locomotion. In E. Meisami and P. S. Timiras (Eds.) Handbook of human growth and developmental biology. Volume I: Part B. CRC Press, Boca Raton, FL.

Rat Somatosensory Cortex

From Wise, Fleshman & Jones (1979) Neuroscience, 4, 1275-1297

Increased opportunities for spatial and temporal summation.

Stehouwer, D.J., McCrea, A.E. & Van Hartesveldt, C. (1994)L-DOPA-induced air-stepping in preweanling rats: II. Kinematicanalyses. Dev. Brain Res., 82, 143-151.

Stehouwer, D.J., McCrea, A.E. & Van Hartesveldt, C. (1994)L-DOPA-induced air-stepping in preweanling rats: II. Kinematicanalyses. Dev. Brain Res., 82, 143-151.

Stehouwer, D.J., McCrea, A.E. & Van Hartesveldt, C. (1994)L-DOPA-induced air-stepping in preweanling rats: II. Kinematicanalyses. Dev. Brain Res., 82, 143-151.

Stehouwer, D.J., McCrea, A.E. & Van Hartesveldt, C. (1994)L-DOPA-induced air-stepping in preweanling rats: II. Kinematicanalyses. Dev. Brain Res., 82, 143-151.

Stehouwer, D.J., McCrea, A.E. & Van Hartesveldt, C. (1994)L-DOPA-induced air-stepping in preweanling rats: II. Kinematicanalyses. Dev. Brain Res., 82, 143-151.

Stehouwer, D.J., McCrea, A.E. & Van Hartesveldt, C. (1994)L-DOPA-induced air-stepping in preweanling rats: II. Kinematicanalyses. Dev. Brain Res., 82, 143-151.

Start BoxClean nest

shavings

Soilednest

shavings

Cleannest

shavings

Soilednest

shavings

Mechanisms ofBehavioral Maturation

Integration and individuationcomplex behaviors emerge when all component partsbecome functional, differentiation of gross behaviors

CNS maturationrequisite circuitry not yet active

Activation of existing circuitrycircuitry present, not active under normal circumstances

Response competitionbehavioral dominance changes with age

Mechanisms ofBehavioral Maturation

Morphological changebehaviors physically not possible

New attractor statesChanging value of control parameters in dynamical systems

Permissive/supportive environmentspecial conditions necessary to allow for behavioral expression

Physiological Maturationphysiological development allows for new solutions to problems

What can we infer about CNS development

from studies of behavior?