topic 3: infancy and brain/sensory/perceptual development

why does brain development in infancy matter

brain development continues through infancy and beyond, and experience shapes the structure of the brain itself

cell body

soma, control center

axon

send message out

dendrite

receive message in

myelin sheath

insulation that speeds up messages

synapse

gap between neurons where communication happens (neurotransmitter released)

the use it or lose it principle

synaptogenesis and synaptic pruning

synaptogenesis

new synapses form rapidly in infancy (12-24mo)

by age 2 appx 15,000 synapses per neuron (way more than in adults)

synaptic pruning

unused synapses get trimmed away (apoptosis - programmed cell death)

synapses used frequently - strengthened and stay

synapses rarely used - pruned away

why do synaptogenesis and synaptic pruning matter in infancy

infant’s early experiences literally shape their brain structure. neglect/enrichment have measurable brain effects

myelin

fatty white coating around axons; looks white under a microscope, hence “white matter”

myelination

process of axons getting wrapping in myelin, starting prenatally but heavily in the first 2 years of life

faster neural transmission =

faster, more coordinated movement and thought

different brain regions mature at ________

different times

4 lobes of the brain

frontal, parietal, temporal, occipital

frontal lobe

planning impulse control, motor movement

parietal lobe

touch and spatial awareness

temporal lobe

hearing and language

occipital lobe

vision

vision matures ____

early; babies see by birth

language regions take _______

longer; toddlers still learning words at age 2-3

the left and right hemispheres specialize for different things (language, spatial), and theyre connected by the ___________. This wiring gets refined through infancy

corpus callosum

cephalocaudal growth pattern

growth from head to torso to legs

head and brain need to grow first, motor control follows the same pattern: head control, trunk control, leg control (babies lift head before torso, torso control before leg control, etc)

proximodistal growth pattern

growth from center to extremities

infants can control their arms before their fingers, grasp with their whole hand before using fingers individually (gross motor skills appear before fine motor skills)

mass to specific growth pattern

moves from large muscle groups to small, precise, muscles (gross motor e.g. rolling, sitting, walking to fine motor e.g. grasping, pinching, feeding self)

a newborn has a massive head compared ot their tiny body, and why ___

they learn to control their neck and smile long before they learn to walk

example of cephalocaudal growth pattern

a baby will learn to wave their entire arm at a toy, then learn to grab it with their whole fist, and only much later master the pincher grasp using just their thumb and index finger

birth weigth

avg 7.5lbs, doubles by 5 mo, triples by 12 mo, quadruples by 24 mo

height

avd birth height 19.5 in, growth 1 in/mo first year then slower

head circumference

appx 14 in, grows 0.4 in/mo first year

strongly correlated with brain growth and cognitive development; used to screen for developmental issues

growth charts

pediatricians use WHO/CDC growth charts (percentile curves) to track kid

consistent growth (even if lower percentile) =

healthy

sudden slowdown in growth =

possible problem

growth as an indicator of health

growth is one of the first tools pediatricians use to detect problems

what abnormal growth might indicate:

• failure to thrive: growth significantly below expected for age

• malnutrition: inadequate calories/nutrients

• health issues: infections, genetic disorders, complications

protective factors

good nutrition, responsive caregiving, safe environment

sleep patterns in infancy

newborns sleep a lot (14-17 hr / day)

REM sleep

rapid eye movement; active sleep (dreaming, brain development happens)

NREM sleep

non-REM; deeper, more restful (3 stages, deepest = stage 3)

newborns ______ REM _________ NREM

50%; 50%

adults ______ REM _______ NREM

20%; 80%

sleep patterns by 6 months

longer stretches of sleep possible (neurologically capable of sleeping 6+ hours)

sleep patterns by 24 months

appx 13-14 hours total (11 hours nighttime, 2-3 hours daytime)

SUID - sudden unexpected infant death

infant dies unexpectedly, often while sleeping

SIDS - sudden infant death syndrome

most common type of SUID (32% in 2020)

other causes of SUID

accidental suffocation (appx 27%)

risk factors for SIDS

• sleeping on stomach or side (vs back)

• soft objects in crib (pillows, blanket, bumper)

• overheating

• bed sharing with substance using or impaired caregiver

• low birth weight, prematurity

SIDS prevention AAP recommendations

• back sleeping first 6-12 mo

• firm sleep surface

• room sharing without bed sharing first 6 mo (ideally 12 mo)

• no soft objects, pillows/blankets in sleep area

• consider pacifier at nap or bed time

• avoid overheating, loose clothing, overdressing

• avoid smoke, alcohol, drug exposure during pregnancy and after birth

• breastfeeding associated with lower SIDS risk

why bedtime routines matter

signals to brain its time to sleep and reduce parental anxiety

ex: bath, quiet music, story, feeding, passive comfort (standing/sitting nearby)

sleep training considerations

approaches vary (ferber method, co sleeping, soothing routines)

cultural and individual family preferences matter

researchers support behavioral interventions for sleep problems

breastfeeding WHO/AAP

exclusive breastfeeding first 6 mo; continue with complementary foods through 12+ mo

benefits of breastfeeding

• digestibility - easier for infant to digest

• immunity - immunoglobulins provide disease protection

• reduction in SIDS risk

• financial - often less expensive than formula

responsive feeding

follow infant’s hunger/fullness cues (sucking, rooting, turning head away)

complimentary feeding (introducing solids)

readiness for solids (appx 6 mo)

• sits upright with minimal support

• brings hand to mouth

• shows interest in food (leans forward, watches others eat)

safe introduction

• one new food every 3-5 days (monitor for allergies)

• start with iron fortified cereals or purees

• progress to soft foods, finger foods as skills develop

flavor learning

• exposure to variety - greater food acceptance

cultural variation

• some cultures introduce solids earlier; different food textures/types used

reflex

automatic, involuntary response to stimulation

purpose of neonatal reflexes

some are for survival (rooting, sucking for feeding) other indicate neurological health

neonatal reflex timeline

most reflexes present at birth, disappear by 12 mo as voluntary motor control develops

key neonatal reflexes

rooting - turn head toward cheek stimulation

sucking - rhythmic sucking on stimulation

moro - sudden extension then flexion of arms

palmar grasp - fingers flex when palm is touched

babinski - extension of big toe on sole stimulation

stepping - alternating stepping movements

motor milestone

significant physical achievement achieved during a predictable age range

milestones show typical ranges, not rigid cutoffs

variation is normal due to genetics, opportunity, culture, practice (e.g. walking 8-17 mo is a very wide range)

age range supports head

6-8 weeks

age range lift head and chest on tummy

2-5 mo

age range roll from tummy to back

4-6 mo

age range sit alone unsupported

4-8 mo

age range stand with support

5-12 mo

age range stand without support

7-17 months

age range walks with support

6-13 months

age range walks without support

8-17 mo

gross motor milestone sequence

appx 12-15 mo - independent walking

14-24 mo- running, climbing, jumping (emerging fine motor coordination)

18-24 months - kicking a ball, throwing, climbing stairs with support

delays in motor milestones can indicate

cerebral palsy, hypotonia (low muscle tone), hypertonia (high muscle tone), genetic disorders, chromosomal conditions, environmental deprivation/neglect

fine motor skills

small muscles controlling precise movement (reaching, grasping, manipulating objects)

fine motor milestone: opens hands briefly

2 mo

fine motor milestone: holds a toy placed in hand; brings hand to mouth

4 mo

fine motor milestone: reaches for a grabs toys

6 mo

fine motor milestone: bangs objects together; transfers objects in between hands

9 mo

fine motor milestone: grasps objects using 2 fingers

12 mo

fine motor milestone: feeds self with fingers

18 mo

fine motor milestone: uses buttons or switches on toys

24 mo

pincer grasp

emerging at appx 9 mo (e.g. can pick up small foods)

sensation

detection of sensory stimuli (physical process: light hits retina, sound hits eardrum, etc)

even newborns have functional sensory systems

perception

interpretation of sensory information (psychological/cognitive process: making sense of what you detect)

perception requires

brain development and learning

it develops over time as the brain matures and experience accumulates

visual acuity development

newborn vision: 20/400 to 20/600 (very blurry), best focus is 8-12 inches away — about distance to mother face while feeding

3 mo: 20/200 (improving)

6 mo: 20/40 to 20/60 (much clearer)\

12 mo: 20/20 (adult like acuity)

why visual acuity develops

fovea (central retina) matures gradually in first 4-6 mo, cones (color receptors) develop, visual cortex (occipital lobe) matures

depth perception

ability to judge if objects are near or far

binocular vision

need both eyes working together to perceive depth (depth cues from eye convergence, binocular disparity)

development of depth perception

by 6 mo, infants can distinguish depth in 2D pictures (3D cues present)

by 6-8 mo, more sophisticated depth perception emerging

findings of the visual cliff experiment

most crawling infants (6-14 mo) refused to cross the deep side, even when mother encouraged them

pre crawling infants (4-6 mo) could be placed on deep side with no fear

implication: fear develops after motor experience (crawling), not before

modern interpretation of visual cliff experiment

motor experience teaches infants about consequences

learning: crawling means you can fall, non-motile infants do not understand this risk yet

cross model integration - vision (dept perception) + motor (crawling experience) + cognition (understanding cause and effect) = caution

baby visual preferences

faces > non faces

curved lines > straight lines

patterns > blank surfaces

new/novel > familiar (habituation effect)

high contrast > low contrast

visual preferences 3-6mo

preference for face intensifies, infants look at eyes more than other facial features

prefer female faces over male faces if primary caregiver is female (familiarity)

why visual preferences matter

babies are not randomly looking, their visual system is biased toward socially relevant stimuli. this supports bonding and learning about people

high amplitude sucking paradigm

give infant special pacifier connected to a computer, measure sucking intensity/frequency, when sucking intensity increases it signals interest in a novel stimulus, use this to test what sounds infants prefer/discriminate

cross modal integration (senses working together)

combining information from multiple sources

reaching for objects: where is it — vision; motor — reach and grasp; proprioception — arm position

coordinating light and sound: looking towards sounds, understanding tat sound comes from source

social interaction: seeing face, hearing voice, feeling touch = understanding “this is a person”

social referencing (looking to others to interpret the world)

infant looks at caregiver’s facial expression or behavior to interpret an ambiguous situation

classic ex: infant encountering a new toy or person looks to parent’s face, if parent smiles (positive) then parent approaches; if parent frowns (negative) then infant withdraws

habituation

infant’s attention decreases when stimulus is repeated (gets bored/used to it)

dishabituation

attention increases when stimulus changes (novelty effect)

preferential looking

present 2 stimuli, measure which one infant looks at longer

works with young infants and tells us about preferences, discrimination, attention

eye tracking

modern technology that records exactly where/how long infant looks

more precise than a human observer measuring, can detect subtle changes in gaze, reveals what captures attention

brain development (synapses, myelation region specialization) enables

motor development, sensory learning, cognitive development