hypernatremia & hyponatremia

8/8/2019 Hypernatremia & hyponatremia

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Hypernat remiaHypernat remia &&

Hyponat remiaHyponat remia

(A Short Review) by DG(A Short Review) by DG GhalanGhalan



HypernatremiaHypernatremia



I n t roduc t ionIn t roduc t ion

It isIt is ananelectrolyteelectrolyte disturbancedisturbance that isthat is

defined by an elevateddefined by an elevated sodiumsodium level inlevel in

the blood.the blood. HypernatremiaHypernatremia is generally notis generally notcaused by an excess of sodium, butcaused by an excess of sodium, but

rather by a relative deficit ofrather by a relative deficit of free waterfree water inin

the body.the body.



For this reason,For this reason, hypernatremiahypernatremia is oftenis often

synonymous with the less precisesynonymous with the less precise

term,term,dehydrationdehydration



Water is lost from the body in a variety of ways,Water is lost from the body in a variety of ways,

includingincluding perspirationperspiration, insensible losses from, insensible losses from

breathing, and in thebreathing, and in the fecesfeces andand urineurine. If the. If theamount of water ingested consistently fallsamount of water ingested consistently falls

below the amount of water lost, the serumbelow the amount of water lost, the serum

sodium level will begin to rise, leading tosodium level will begin to rise, leading to

hypernatremiahypernatremia. Rarely,. Rarely, hypernatremiahypernatremia cancanresult from massiveresult from massive saltsalt ingestion, such as mayingestion, such as may

occur from drinkingoccur from drinking seawaterseawater..



Ordinarily, even a small rise in the serumOrdinarily, even a small rise in the serumsodium concentration above the normal rangesodium concentration above the normal range

results in a strong sensation ofresults in a strong sensation of thirstthirst, an, anincrease in free water intake, and correction ofincrease in free water intake, and correction ofthe abnormality. Therefore,the abnormality. Therefore, hypernatremiahypernatremiamost often occurs in people such asmost often occurs in people such as infantsinfants,,those with impairedthose with impaired mental statusmental status, or the, or the

elderly, who may have an intact thirstelderly, who may have an intact thirstmechanism but are unable to ask for or obtainmechanism but are unable to ask for or obtainwater.water.



Et io logyEt io logy

(1.)Hypovolemic(1.)Hypovolemic

Inadequate intake of water, typically in elderlyInadequate intake of water, typically in elderly

or otherwise disabled patients who are unableor otherwise disabled patients who are unableto take in water as their thirst dictates. This isto take in water as their thirst dictates. This isthe most common cause ofthe most common cause of hypernatremiahypernatremia..

Excessive losses of water from the urinaryExcessive losses of water from the urinarytract, which may be caused bytract, which may be caused by glycosuriaglycosuria, or, or

other osmotic diuretics.other osmotic diuretics. Water losses associated with extremeWater losses associated with extreme

sweating.sweating.

Severe watery diarrheaSevere watery diarrhea



(2.)(2.) EuvolemicEuvolemic::

Excessive excretion of water from theExcessive excretion of water from the

kidneys causedkidneys caused bybydiabetesdiabetes insipidusinsipidus,,

which involves either inadequatewhich involves either inadequate

production of the hormone,production of the hormone, vasopressinvasopressin,,

from the pituitary gland or impairedfrom the pituitary gland or impairedresponsiveness of the kidneys toresponsiveness of the kidneys to

vasopressin.vasopressin.



(3.)(3.) HypervolemicHypervolemic::

Intake of aIntake of a hypertonichypertonic fluid (a fluid with a higherfluid (a fluid with a higherconcentration of solutes than the remainder of theconcentration of solutes than the remainder of the

body). This is relatively uncommon, though it can occurbody). This is relatively uncommon, though it can occurafter a vigorous resuscitation where a patient receivesafter a vigorous resuscitation where a patient receivesa large volume of aa large volume of a concentratedconcentratedsodiumsodiumbicarbonatebicarbonate solution. Ingestingsolution. Ingesting seawaterseawater also causesalso causeshypernatremiahypernatremia because seawater is hypertonic.because seawater is hypertonic.

MineralcorticoidMineralcorticoid excess due to a disease state suchexcess due to a disease state suchasas Conn's syndromeConn's syndrome oror Cushing's DiseaseCushing's Disease



Symptoms:Symptoms:

Clinical manifestations ofClinical manifestations of hypernatremiahypernatremia

can be subtle, consistingcan be subtle, consisting ofoflethargylethargy,,

weakness, irritability, andweakness, irritability, and edemaedema. With. Withmore severe elevations of the sodiummore severe elevations of the sodium

level,level, seizuresseizures andand comacoma may occur.may occur.



Severe symptoms are usually due toSevere symptoms are usually due toacute elevation of the plasma sodiumacute elevation of the plasma sodium

concentration to above 158concentration to above 158 mEqmEq /L /L(normal is typically about 135(normal is typically about 135--145145mEqmEq /L). Values above 180 /L). Values above 180 mEqmEq /L are /L areassociated with a high mortality rate,associated with a high mortality rate,

particularly in adults. However such highparticularly in adults. However such highlevels of sodium rarely occur withoutlevels of sodium rarely occur withoutsevere coexisting medical conditions.severe coexisting medical conditions.



Trea tment :T rea tment :

The cornerstone of treatment isThe cornerstone of treatment isadministration of free water to correct theadministration of free water to correct the

relative water deficit. Water can berelative water deficit. Water can bereplaced orally orreplaced orally or intravenouslyintravenously..However, overly rapid correction ofHowever, overly rapid correction ofhypernatremiahypernatremia is potentially veryis potentially very

dangerous. The body (in particulardangerous. The body (in particularthethe brainbrain) adapts to the higher sodium) adapts to the higher sodiumconcentration.concentration.



Rapidly lowering the sodium concentration withRapidly lowering the sodium concentration withfree water, once this adaptation has occurred,free water, once this adaptation has occurred,

causes water to flow into brain cells andcauses water to flow into brain cells andcauses them to swell. This can lead tocauses them to swell. This can lead to cerebralcerebraledemaedema, potentially resulting in seizures,, potentially resulting in seizures,permanentpermanent brain damagebrain damage, or death. Therefore,, or death. Therefore,significantsignificant hypernatremiahypernatremia should be treatedshould be treated

carefully bycarefully by aaphysicianphysician or other medicalor other medicalprofessional with experience in treatmentprofessional with experience in treatmentofofelectrolyteelectrolyte imbalancesimbalances..



HyponatremiaHyponatremia



I n t roduc t ion :In t roduc t ion :

It is an electrolyte disturbance in whichIt is an electrolyte disturbance in which

the sodium concentration in thethe sodium concentration in the serumserumisis

lower than normal. Sodium is thelower than normal. Sodium is thedominant extracellulardominant extracellular cationcation and cannotand cannot

freely cross the cell membrane. Itsfreely cross the cell membrane. Its

homeostasis is vital to the normalhomeostasis is vital to the normalphysiologic function of cells.physiologic function of cells.



Normal serum sodium levels are betweenNormal serum sodium levels are between

135135--145145 mEqmEq /L. /L. HyponatremiaHyponatremia is definedis defined

as a serum level of less than 135as a serum level of less than 135 mEqmEq /L /Land is considered severe when theand is considered severe when the

serum level is below 125serum level is below 125 mEqmEq /L. /L.



HyponatremiaHyponatremia is most often a complication ofis most often a complication of

other medical illnesses in which either fluidsother medical illnesses in which either fluids

rich in sodium are lost (for example because ofrich in sodium are lost (for example because ofdiarrhea or vomiting) or excess waterdiarrhea or vomiting) or excess water

accumulates in the body at a higher rate thanaccumulates in the body at a higher rate than

can be excreted (for example incan be excreted (for example in congestivecongestive

heart failureheart failure, syndrome of inappropriate, syndrome of inappropriateantidiureticantidiuretic hormone,hormone, SIADHSIADH,, ororpolydipsiapolydipsia).).



Regarding sodium loss as a cause ofRegarding sodium loss as a cause of

hyponatremiahyponatremia, it is important to note that, it is important to note that

such losses promotesuch losses promote hyponatremiahyponatremia ininonly an indirect manner. In particular,only an indirect manner. In particular,

hyponatremiahyponatremia occurring in associationoccurring in association

with sodium loss does not reflectwith sodium loss does not reflect

inadequate sodium availability as a resultinadequate sodium availability as a result

of the losses.of the losses.



Rather, the sodium loss leads to a stateRather, the sodium loss leads to a state

of volume depletion, with volumeof volume depletion, with volume

depletion serving as signal for thedepletion serving as signal for therelease of ADH (release of ADH (antianti--diuretic hormonediuretic hormone).).

As a result of ADHAs a result of ADH--stimulated waterstimulated water

retention, blood sodium becomes dilutedretention, blood sodium becomes diluted

andand hyponatremiahyponatremia results.results.



HyponatremiaHyponatremia can also affect athletescan also affect athletes

who consume too much fluid duringwho consume too much fluid during

enduranceendurance events,peopleevents,people who fast onwho fast on juice or water for extended periods and juice or water for extended periods and

people whose dietary sodium intake ispeople whose dietary sodium intake is

chronically insufficient.chronically insufficient.



Frequency:Frequency:

HyponatremiaHyponatremia is the most common electrolyteis the most common electrolyte

disorder. Its frequency is higher in females, thedisorder. Its frequency is higher in females, the

elderly, and in patients that are hospitalized.elderly, and in patients that are hospitalized.The incidence ofThe incidence of hyponatremiahyponatremia dependsdepends

largely on the patient population. A hospitallargely on the patient population. A hospital

incidence of 15incidence of 15--20% is common, while only 320% is common, while only 3--

5% of patients who are hospitalized have a5% of patients who are hospitalized have aserum sodium level of less than 130serum sodium level of less than 130 mEqmEq /L. /L.



HyponatremiaHyponatremia has been reported in up tohas been reported in up to

30% of elderly patients in nursing homes30% of elderly patients in nursing homes

and is also present in approximately 30%and is also present in approximately 30%of depressed patients onof depressed patients on selectiveselective

serotonin reuptake inhibitorsserotonin reuptake inhibitors..



Symptoms:Symptoms:

Symptoms ofSymptoms of hyponatremiahyponatremia include nauseainclude nauseaand vomiting, headache, confusion, lethargy,and vomiting, headache, confusion, lethargy,fatigue, appetite loss, restlessness andfatigue, appetite loss, restlessness andirritability, muscle weakness, spasms, orirritability, muscle weakness, spasms, orcramps, seizures, and decreasedcramps, seizures, and decreasedconsciousness or coma. The presence andconsciousness or coma. The presence andseverity of symptoms are associated with theseverity of symptoms are associated with the

level of serum sodium, with the lowest levels oflevel of serum sodium, with the lowest levels ofserum sodium associated with the moreserum sodium associated with the moreprominent and serious symptoms.prominent and serious symptoms.



However, emerging data suggests thatHowever, emerging data suggests that

mildmild hyponatremiahyponatremia (serum sodium levels(serum sodium levels

at 131at 131 mEqmEq /L or above) is associated /L or above) is associatedwith numerous complications andwith numerous complications and

undiagnosed symptoms.undiagnosed symptoms.



Many medical illnesses, such asMany medical illnesses, such as

congestive heart failure, liver failure,congestive heart failure, liver failure,

renal failure, or pneumonia may berenal failure, or pneumonia may beassociated withassociated with hyponatremiahyponatremia. These. These

patients frequently present because ofpatients frequently present because of

primary diseaseprimary disease symptomatologysymptomatology and areand are

diagnosed after presenting due todiagnosed after presenting due to

manifestations of other medical issues.manifestations of other medical issues.



Neurological symptoms often show forNeurological symptoms often show for

extremely low levels of sodium. Whenextremely low levels of sodium. When

sodium levels in blood become too low,sodium levels in blood become too low,excess water enters cells and causes theexcess water enters cells and causes the

cells to swell. Swelling in the brain iscells to swell. Swelling in the brain is

especially dangerous because the brainespecially dangerous because the brain

is confined by the skull and is unable tois confined by the skull and is unable to

expand.expand.



Neurological symptoms most often areNeurological symptoms most often aredue to very low serum sodium levelsdue to very low serum sodium levels

(usually <115(usually <115 mEqmEq /L), resulting in /L), resulting inintracerebralintracerebral osmotic fluid shifts andosmotic fluid shifts andbrain edema. This neurological symptombrain edema. This neurological symptomcomplex can lead tocomplex can lead to tentorialtentorial herniationherniation

with subsequent brain stem compressionwith subsequent brain stem compressionand respiratory arrest, resulting in deathand respiratory arrest, resulting in deathin the most severe cases.in the most severe cases.



The severity of neurological symptomsThe severity of neurological symptomscorrelates with the rapidity and severity of thecorrelates with the rapidity and severity of thedrop in serum sodium. A gradual drop, even todrop in serum sodium. A gradual drop, even tovery low levels, may be tolerated well if itvery low levels, may be tolerated well if itoccurs over several days or weeks, because ofoccurs over several days or weeks, because ofneuronal adaptation. The presence ofneuronal adaptation. The presence ofunderlying neurological disease, like a seizureunderlying neurological disease, like a seizure

disorder, or nondisorder, or non--neurological metabolicneurological metabolicabnormalities, also affects the severity ofabnormalities, also affects the severity ofneurologic symptoms.neurologic symptoms.



Examina t ionExamina t ion

Examination should include orthostaticExamination should include orthostaticvital signs and an accurate assessmentvital signs and an accurate assessment

of volume status. This determination (i.e.of volume status. This determination (i.e.hypervolemichypervolemic,, euvolemiceuvolemic,, hypovolemichypovolemic))often guides treatment decisions. A fulloften guides treatment decisions. A fullassessment of medicalassessment of medical comorbiditycomorbidity alsoalso

is essential, with particular attention paidis essential, with particular attention paidto cardiopulmonary and neurologicalto cardiopulmonary and neurologicalcomponents of the examination.components of the examination.



Types o f oc c urrenc eTypes o f oc c urrenc e

(I)(I) Hypervolemic Hypervolemic hyponatremia hyponatremia ::

excess water dilutes the sodiumexcess water dilutes the sodium

concentration, causing low sodium levels.concentration, causing low sodium levels.HypervolemicHypervolemic hyponatremiahyponatremia is commonlyis commonly

the result of kidney failure, heart failure orthe result of kidney failure, heart failure or

liver failure.liver failure.



(II)(II) Euvolemic Euvolemic hyponatremia hyponatremia :: normalnormal

water levels are combined with lowwater levels are combined with low

sodium levels. This condition issodium levels. This condition iscommonly due to chronic healthcommonly due to chronic health

conditions, cancer or certain medications.conditions, cancer or certain medications.



( ( III)Hypovolemic III)Hypovolemic hyponatremia hyponatremia ::

water and sodium levels are both low.water and sodium levels are both low.

This may occur, for example, whenThis may occur, for example, whenexercising in the heat withoutexercising in the heat without

replenishing fluid electrolytes or withreplenishing fluid electrolytes or with

marked blood loss.marked blood loss.



InIn Chronic Chronic hyponatremia hyponatremia sodium levels dropsodium levels drop

gradually over several days or weeks andgradually over several days or weeks and

symptoms and complications are typicallysymptoms and complications are typically

moderate. Chronicmoderate. Chronic hyponatremiahyponatremia is often calledis often called

asymptomaticasymptomatic hyponatremiahyponatremia in clinical settingsin clinical settingsbecause it is thought to have no symptoms;because it is thought to have no symptoms;

however, emerging data suggests thathowever, emerging data suggests that

““asymptomaticasymptomatic”” hyponatremiahyponatremia is not actuallyis not actually

asymptomatic.asymptomatic.



InIn Acute Acute hyponatremia hyponatremia sodium levelssodium levels

drop rapidly, resulting in potentiallydrop rapidly, resulting in potentially

dangerous effects, such as rapid braindangerous effects, such as rapid brainswelling, which can result in coma andswelling, which can result in coma and

death.death.



Causes:Causes:

Many possible conditions and lifestyle factorsMany possible conditions and lifestyle factors

can lead tocan lead to hyponatremiahyponatremia, including:, including:

Syndrome of inappropriate anti Syndrome of inappropriate anti - - diuretic diuretic hormone (SIADH).hormone (SIADH). In this condition, high levelsIn this condition, high levels

of the antiof the anti--diuretic hormone (ADH) arediuretic hormone (ADH) are

produced, causing the body to retain waterproduced, causing the body to retain water

instead of excreting it in urine.instead of excreting it in urine. Cirrhosis Cirrhosis . Liver disease can cause fluids to. Liver disease can cause fluids to

accumulate in the body.accumulate in the body.



Kidney problems Kidney problems . Kidney failure and other. Kidney failure and other

kidney diseases can render the body unable tokidney diseases can render the body unable to

efficiently remove excess fluids from the body.efficiently remove excess fluids from the body. Congestive heart failure Congestive heart failure . This condition causes. This condition causes

the abdomen and lower extremities to retainthe abdomen and lower extremities to retain

fluids.fluids.

Water pills (diuretics),Water pills (diuretics), especiallyespecially thiazidethiazidediuretics. Diuretics work by making the bodydiuretics. Diuretics work by making the body

excrete more sodium in urineexcrete more sodium in urine



Consuming excessive water during Consuming excessive water during

exercise ( exercise ( exertional exertional hyponatremia hyponatremia

or or exercise exercise - - associated associated hyponatremia hyponatremia ( ( EAH)).EAH)).BecauseBecause sodium issodium is

lost through sweat, drinking too muchlost through sweat, drinking too much

water during endurance activities, suchwater during endurance activities, such

as marathons and triathlons, can diluteas marathons and triathlons, can dilute

sodium content in blood.sodium content in blood.



Hormonal changes due to Hormonal changes due to adrenal gland adrenal gland insufficiency (Addison insufficiency (Addison ’ ’ s disease).s disease). AdrenalAdrenalglands produce hormones that help maintainglands produce hormones that help maintainthe bodythe body’’s balance of sodium, potassium ands balance of sodium, potassium andwater.water.

Hormonal changes due to an under active Hormonal changes due to an under active thyroid ( thyroid ( hypothyroidism hypothyroidism ). ).

Primary Primary polydipsia polydipsia . In this condition, thirst. In this condition, thirstincreases significantly, causing a person toincreases significantly, causing a person todrink excessive amounts of fluid.drink excessive amounts of fluid.



Certain medications Certain medications . Some medications,. Some medications,particularlyparticularly selective serotonin reuptakeselective serotonin reuptakeinhibitorsinhibitors and some pain medications, cause aand some pain medications, cause aperson to urinate or perspire more than normal.person to urinate or perspire more than normal.

The recreational drug The recreational drug MDMAMDMA. This. Thisamphetamine causes a ripple effect on theamphetamine causes a ripple effect on thebodybody’’s ADH and water levels thats ADH and water levels that — —especiallyespecially

in combination with heavy drinkingin combination with heavy drinking — —increasesincreasesthe risk of severe and even fatal cases ofthe risk of severe and even fatal cases ofhyponatremiahyponatremia..



Chronic, severe vomiting or diarrhea Chronic, severe vomiting or diarrhea . This. This

causes the body to lose fluids and electrolytes,causes the body to lose fluids and electrolytes,

including sodium.including sodium. Dehydration Dehydration . In dehydration, the body loses. In dehydration, the body loses

fluids and electrolytes.fluids and electrolytes.

Diet.Diet. A lowA low--sodium, highsodium, high--water diet can disturbwater diet can disturb

the proper balance between sodium and fluidsthe proper balance between sodium and fluidsin the blood. Excessive intake of diuretics,in the blood. Excessive intake of diuretics,

including beer, can have the same effect.including beer, can have the same effect.



Risk Fac t ors :Risk Fac t ors :

Age Age .. Low blood sodium is more common inLow blood sodium is more common in

older adults. Contributing factors include ageolder adults. Contributing factors include age--

related changes and a greater likelihood ofrelated changes and a greater likelihood ofdeveloping a chronic disease that impairs thedeveloping a chronic disease that impairs the

bodybody’’s sodium balance.s sodium balance.

Diet Diet .. A person may be at an increased risk ofA person may be at an increased risk of

hyponatremiahyponatremia if he is following a lowif he is following a low--sodiumsodiumdiet, especially in combination with drinkingdiet, especially in combination with drinking

diuretic beverages.diuretic beverages.



Intensive physical activities Intensive physical activities .. People whoPeople whodrink too much water while taking part indrink too much water while taking part in

marathons, triathlons, Iron Manmarathons, triathlons, Iron Mancompetitions and other longcompetitions and other long--distance,distance,highhigh--intensity activities are at anintensity activities are at anincreased risk ofincreased risk of hyponatremiahyponatremia..

Climate Climate .. New exposure to hot weatherNew exposure to hot weathercan increase the amount of sodium acan increase the amount of sodium aperson loses through sweating.person loses through sweating.



Certain drugs Certain drugs . Medications that increase. Medications that increase

risk ofrisk of hyponatremiahyponatremia includeinclude thiazidethiazide

diuretics and selective serotonin reuptakediuretics and selective serotonin reuptakeinhibitors and pain medications thatinhibitors and pain medications that

cause a patient to urinate or perspirecause a patient to urinate or perspire

more than usual. In addition, themore than usual. In addition, the

recreational drug MDMA has been linkedrecreational drug MDMA has been linked

to fatal cases ofto fatal cases of hyponatremiahyponatremia. .. .



Compl ica t ion :Compl ica t ion :

ChronicChronic hyponatremiahyponatremia can lead to suchcan lead to such

complications as neurological impairments.complications as neurological impairments.

These neurological impairments most oftenThese neurological impairments most oftenaffect gait and attention and can lead to falls,affect gait and attention and can lead to falls,

osteoporosis, and decreased reaction time.osteoporosis, and decreased reaction time.

Complications for chronicComplications for chronic hyponatremiahyponatremia areare

most dangerous for geriatric patients. Falls aremost dangerous for geriatric patients. Falls arethe leading cause of deaths related to injurythe leading cause of deaths related to injury

among people 65 years or older.among people 65 years or older.



In a recent studyIn a recent study the incidence ofthe incidence of hyponatremiahyponatremia ininelderly patients with largeelderly patients with large--bone fractures was morebone fractures was morethan double that of nonthan double that of non--fracture patients. Recent workfracture patients. Recent work

byby VerbalisVerbalis etcetc suggests thatsuggests that hyponatremiahyponatremia inducesinducesosteoporosis and found the adjusted odds ratio forosteoporosis and found the adjusted odds ratio fordeveloping osteoporosis to be 2.87 times higherdeveloping osteoporosis to be 2.87 times higheramong adults with mildamong adults with mild hyponatremiahyponatremia compared tocompared tothose without.those without.

AcuteAcute hyponatremiahyponatremia can lead to much more seriouscan lead to much more seriouscomplications including brain disease, braincomplications including brain disease, brain herniationherniation,,cardiopulmonary arrest, cerebral edema, seizures,cardiopulmonary arrest, cerebral edema, seizures,coma, and death.coma, and death.



Trea tment :T rea tment :

The treatment ofThe treatment of hyponatremiahyponatremia oftenoften

depends on the underlying cause. If adepends on the underlying cause. If a

person is truly asymptomatic or has onlyperson is truly asymptomatic or has onlysubtle symptoms, little treatment othersubtle symptoms, little treatment other

than water restriction may be required. Inthan water restriction may be required. In

a setting of volume depletion,a setting of volume depletion,

intravenous administration of normalintravenous administration of normal

saline may be effective.saline may be effective.



Pharmaceutically,Pharmaceutically, vasopressin receptorvasopressin receptorantagonistsantagonists can be used in the treatmentcan be used in the treatment

ofof hyponatremiahyponatremia, especially in patients, especially in patientswith congestive heart failure or liverwith congestive heart failure or livercirrhosis. A vasopressin receptorcirrhosis. A vasopressin receptorantagonist is an agent that interferes withantagonist is an agent that interferes with

the action at the vasopressin receptors.the action at the vasopressin receptors.Vasopressin is also known as ADH, theVasopressin is also known as ADH, theantianti--diuretic hormone.diuretic hormone.



A new class of medication, theA new class of medication, the ““vaptanvaptan”” drugsdrugshas been specifically developed to inhibit thehas been specifically developed to inhibit theaction of vasopressin on its receptors (V1A,action of vasopressin on its receptors (V1A,

V1B, and V2). These receptors have a varietyV1B, and V2). These receptors have a varietyof functions, with the V1A and V2 receptors areof functions, with the V1A and V2 receptors areexpressed peripherally and involved in theexpressed peripherally and involved in themodulation of blood pressure and kidneymodulation of blood pressure and kidneyfunction respectively, while the V1A and V1Bfunction respectively, while the V1A and V1B

receptors are expressed in the central nervousreceptors are expressed in the central nervoussystem. V1A is expressed in many regions ofsystem. V1A is expressed in many regions ofthe brain, and has been linked to a variety ofthe brain, and has been linked to a variety ofsocial behaviors in humans and animals.social behaviors in humans and animals.



(Reference: Wikipedia)(Reference: Wikipedia)

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