Lecture 4: Memory in Temporal Lobe Epilepsy (TLE)

Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy and accounts for around 60% of focal epilepsies. Around 30% of cases are resistant to medication, meaning seizures continue despite treatment. In children with severe TLE, surgery is often considered because long-term seizure freedom is unlikely with medication alone.

TLE is especially important in neuropsychology because the temporal lobes contain structures critical for declarative memory, particularly episodic and semantic memory. Surgery to control seizures often involves removal of temporal lobe structures, including parts of the hippocampus and temporal neocortex, so understanding the cognitive consequences is essential.

Clinical Features of Temporal Lobe Epilepsy

Children with TLE often experience seizures with experiential or sensory symptoms before loss of awareness occurs. These early focal symptoms are called auras.

Typical seizure experiences include:

• déjà vu

• dream-like feelings

• altered perception of reality

• unusual bodily sensations

• taste or smell distortions

• emotional changes

• inability to understand speech despite hearing it

These symptoms occur because seizure activity spreads through limbic and temporal lobe networks involved in memory, emotion, sensation, and perception.

Seizures may initially occur with preserved awareness but can later progress into more motor manifestations such as:

• stiffening of limbs

• eye movements

• tonic-clonic seizures

• impaired consciousness

Children often struggle to describe these sensations clearly, making diagnosis more difficult than in adults.

Underlying Pathology in TLE

Several structural abnormalities commonly underlie paediatric TLE:

Hippocampal Sclerosis (HS)

Hippocampal sclerosis involves atrophy and scarring of the hippocampus. It is strongly associated with severe memory impairment because the hippocampus is central to episodic memory formation.

Developmental Tumours (DNETs)

Dysembryoplastic neuroepithelial tumours (DNETs) is a rare, benign (WHO Grade 1) slow-growing brain tumor.They are Benign developmental tumours commonly associated with childhood epilepsy. Unlike HS, the hippocampus may remain structurally intact, which has important consequences for memory outcome.

Cortical Dysplasia

Cortical dysplasia refers to abnormal cortical development and organisation. These malformed cortical areas can generate epileptic activity.

Why Surgery is Used

Approximately 25% of epilepsy surgery procedures in children are performed for TLE.

Surgery is considered because:

• many children remain highly seizure-active despite multiple medications

• chronic seizures negatively affect cognition and development

• surgery can produce long-term seizure freedom

• reducing seizures may improve developmental trajectories

However, surgery carries risks because temporal lobe structures critical for memory may be removed.

The major neuropsychological challenge is balancing:

• seizure control
  vs

• preservation of cognitive function

Key Research Questions in Paediatric TLE

Major questions include:

1. How can clinicians best inform families about cognitive and educational outcomes?

2. How can surgery be optimised to maximise benefit and minimise cognitive harm?

3. What drives long-term developmental changes?

Important factors influencing outcomes include:

• seizure freedom

• freedom from anti-epileptic medication

• lesion size and location

• white and grey matter integrity

• extent of surgical resection

Researchers aim to identify modifiable factors so surgical procedures can be refined to improve outcomes while minimising cognitive consequences.

Declarative Memory and the Temporal Lobes

Declarative memory refers to consciously accessible memory.

It has two major components:

1. Episodic memory

2. Semantic memory

Episodic Memory

Episodic memory refers to autobiographical experiences tied to a unique time and place.

Examples include:

• what you ate for breakfast

• your last birthday

• where you were during a major event

Episodic memory involves remembering personally experienced events situated in context.

The hippocampus is considered the most critical structure for episodic memory. Damage to the hippocampus produces severe impairment in forming or retrieving episodic memories.

Semantic Memory

Semantic memory refers to general world knowledge that is not tied to a specific event.

Examples include:

• word meanings

• facts

• object knowledge

• names of people

• concepts

Unlike episodic memory, semantic memory is shared culturally and is independent of time and place.

Material Specificity: Verbal vs Visual Memory

Temporal lobe functions also show material specificity.

Left Temporal Lobe

The left temporal lobe is more associated with:

• verbal memory

• language

• semantic processing

Right Temporal Lobe

The right temporal lobe is more associated with:

• visual memory

• visuospatial processing

• navigation

• non-verbal memory

One example described a patient whose knitting ability deteriorated after right temporal surgery because spatial representations were impaired.

However, this left-right distinction is less clear in children because developmental lateralisation is still evolving.

Developmental Amnesia and the Hippocampus

Developmental amnesia (DA) provides strong evidence for the role of the hippocampus in episodic memory.

Children with developmental amnesia typically have:

• severe episodic memory impairment

• relatively preserved semantic memory

MRI images demonstrate marked hippocampal damage compared with healthy controls.

This dissociation is important because it demonstrates that:

• episodic and semantic memory are partly separable systems

• the hippocampus is especially crucial for episodic memory

Semantic memory can still develop despite severe hippocampal injury because semantic knowledge becomes distributed across cortical systems over time.

Organisation of Semantic Memory

Two major theories explain semantic memory organisation.

Distributed-Only Model

Semantic knowledge is distributed across multiple cortical areas depending on the type of information:

• colour information

• movement

• sound

• action

• shape

Different sensory and motor systems contribute to semantic representations.

Distributed-Plus-Hub Model

This model proposes that information is distributed but integrated through a central semantic “hub”.

The anterior temporal lobe (ATL), especially the temporal pole, is thought to function as this hub.

Semantic Dementia and the Temporal Pole

Evidence for the ATL semantic hub comes from semantic dementia.

Semantic dementia is a neurodegenerative disorder involving anterior temporal lobe degeneration.

Patients show:

• severe loss of conceptual knowledge

• inability to identify objects or meanings

• relatively preserved episodic memory early on

Patients may no longer understand what a “dog” is despite otherwise coherent cognition.

This strongly suggests the temporal poles are critical for semantic memory access.

Hierarchical Organisation of Memory

The memory system is organised hierarchically.

Episodic Memory Network

The episodic memory system includes:

• hippocampus (HPC)

• entorhinal cortex

• perirhinal cortex

• parahippocampal cortex

Inputs arrive through ventral and dorsal processing streams before being integrated within hippocampal circuits.

Semantic Memory Network

Semantic memory relies more heavily on the anterior temporal lobe and distributed cortical representations.

Predicting Memory Profiles in Paediatric TLE

Researchers investigated whether memory deficits could be predicted based on:

• left vs right lesions

• hippocampal sclerosis vs DNET tumours

Groups included:

• left hippocampal sclerosis (left HS)

• right hippocampal sclerosis (right HS)

• left dysembryoplastic neuroepithelial tumour (left DNET)

• right dysembryoplastic neuroepithelial tumour (right DNET)

• developmental amnesia (DA)

Cormack et al. (2011): Memory in Children with TLE

This study investigated short-term, semantic, and episodic memory in paediatric TLE.

Findings

1. Hippocampal sclerosis caused major episodic memory impairment

Children with HS showed substantial impairment in verbal episodic memory regardless of whether the lesion was left or right sided.

This was unexpected because adult neuropsychology predicts stronger lateralised effects.

The findings suggest paediatric memory systems are less strongly lateralised than adult systems.

2. DNT group showed preserved episodic memory

Children with DNTs generally retained better episodic memory because the hippocampus remained structurally intact.

This demonstrates the critical role of hippocampal integrity in episodic memory.

3. Left anterior temporal lesions impaired semantic memory

Children with left anterior temporal DNT lesions showed poorer semantic memory.

This supports the idea that the anterior temporal lobe acts as a semantic hub.

4. Short-term memory remained relatively preserved

Digit span performance was largely normal.

This suggests working memory systems are less dependent on hippocampal structures.

Working memory is therefore not the primary concern in TLE.

Why Are Deficits More Widespread Than Expected?

Children with unilateral hippocampal lesions often show bilateral or widespread cognitive impairment.

Researchers proposed that TLE affects broader brain networks rather than isolated structures.

The hippocampus has extensive connections with:

• frontal lobes

• retrosplenial cortex

• limbic regions

• contralateral temporal structures

As a result, epilepsy may disrupt distributed cognitive systems.

Neural Correlates of Cognitive Impairment

Voxel-based morphometry studies found:

• grey matter reductions in regions connected to the atrophic hippocampus

• bilateral limbic system atrophy

Cormack (2005) demonstrated focal grey matter reductions connected to the damaged hippocampus.

Duzel et al. (2006) showed widespread limbic atrophy in unilateral adult TLE.

These findings support the idea that TLE is a network disorder rather than purely focal pathology.

White Matter Changes in TLE

Diffusion imaging studies reveal widespread white matter abnormalities extending beyond the temporal lobe.

Changes are found in:

• temporal pathways

• limbic tracts

• commissural fibres

• corticospinal pathways

Lesion-negative TLE often produces even more bilateral and diffuse white matter abnormalities than hippocampal sclerosis.

“Lesion-negative” means that standard MRI scans do not show a clear visible structural abnormality that explains the epilepsy.

This is important because processing speed reductions and broader cognitive difficulties may reflect widespread white matter disruption rather than only focal lesions.

Lesion-Negative TLE

Some patients have severe epilepsy despite no visible lesion on MRI.

This is called lesion-negative TLE.

Even advanced MRI may fail to identify abnormalities in 15–20% of severe epilepsy cases.

To detect subtle abnormalities clinicians may use:

• PET scans

• functional imaging

• morphometric MRI analysis

• AI-assisted detection algorithms

Memory Across the Lifespan in TLE

Studies show that memory difficulties accumulate across development.

Helmstaedter & Elger (2009) found that memory performance increasingly diverges from healthy controls over time.

Example trajectory:

• Age 6: mean cognitive level ≈ 100

• Age 17: ≈ 87

• Age 23: ≈ 81

This suggests untreated epilepsy progressively disrupts developmental gains.

Patients tend to lag further behind normal developmental trajectories over time rather than simply losing previously acquired skills.

TLE and Accelerated Cognitive Ageing

Adults with epilepsy may show earlier cognitive decline and increased risk of dementia-like processes.

Research suggests:

• earlier cognitive deterioration

• abnormal ageing trajectories

• possible links to tau accumulation

Early-onset epilepsy appears particularly harmful because it disrupts brain development during sensitive developmental periods.

Intellectual Development in Childhood Epilepsy

Children with TLE show highly variable intellectual outcomes, but many fall below average IQ ranges.

Important predictors include:

• earlier seizure age onset

• longer epilepsy duration

Children with onset during the first years of life are particularly vulnerable.

Some children become non-verbal or untestable despite relatively focal lesions, suggesting epilepsy can profoundly affect broader developmental processes.

The concern is not just the seizure itself.

Early-onset epilepsy is often associated with:

• more severe underlying brain abnormalities

• longer duration of uncontrolled seizures

• medication exposure over many years

• disrupted sleep and learning

All of these combine to affect development.

Factors Affecting Cognitive Development

Cognitive difficulties in epilepsy are not caused solely by seizures themselves.

Additional contributing factors include:

• chronic seizure activity

• sleep disruption

• anti-epileptic medication side effects

• missed schooling

• reduced educational opportunities

• social disruption

These factors interact with underlying brain pathology to influence long-term outcomes.

In epilepsy, chronic seizure activity means seizures are happening repeatedly over an extended period, such as months or years.

Developmental Trajectories After Surgery

The developmental model presented proposes several possible outcomes after epilepsy surgery.

Trajectory A

Development continues at a parallel but delayed rate.

Children remain below peers but no longer deteriorate.

Trajectory B

Ongoing developmental slowing or stagnation.

Trajectory C

Improved developmental trajectory with partial catch-up.

A stable IQ after surgery can actually represent a positive outcome in childhood because it means the child is continuing to develop at the same rate as peers rather than falling further behind.

This is a critical developmental concept:

In children, maintaining a stable IQ score often reflects preserved developmental progression rather than lack of improvement.

Reorganisation and Plasticity

Children may show functional reorganisation after early temporal lobe injury.

Possible changes include:

• language reorganisation

• atypical language lateralisation

• reorganisation of verbal memory systems

However, reorganisation is incomplete and variable between individuals.

This highlights the complexity of paediatric neuroplasticity.

Pre- to Post-Surgical Cognition in Paediatric Temporal Lobe Epilepsy

The major goal of epilepsy surgery is seizure freedom. Reducing or eliminating seizures can improve quality of life, educational participation, independence, and long-term cognitive development. Surgery is particularly important in children because the developing brain still has significant plasticity and may recover functions over time.

An important idea throughout this topic is that cognition in epilepsy is developmental rather than static. Children with ongoing epilepsy often fall progressively further behind typical developmental trajectories. Successful surgery may allow children to stabilise, partially catch up, or in some cases develop more rapidly afterwards.

Long-Term Cognitive Outcome After Epilepsy Surgery

Several major longitudinal studies examined long-term outcomes after childhood epilepsy surgery:

• Skirrow et al. Neurology (2011)

• Skirrow et al. Brain (2015)

• Skirrow et al. Epilepsia (2018)

• Eriksson et al. Brain (2024)

These studies followed children for many years after surgery and showed that surgery can alter long-term developmental trajectories.

Study 1: Long-Term IQ Outcome After Surgery

Study Characteristics

• 42 surgical patients

• mean age at surgery: 13 years

• mean age at follow-up: 23 years

• follow-up period ≈ 9 years

• non-surgical comparison group included

Main Findings

The surgery group showed a shift towards higher IQ ranges at long-term follow-up.

IQ increases

• 26% of surgical patients gained more than 15 IQ points

• no control patients showed this degree of gain

IQ decreases

• only 2% of surgical patients showed significant IQ decline

The largest gains occurred in children who were functioning in lower IQ ranges before surgery. Children already functioning in average or higher ranges tended to remain relatively stable.

Functional Outcomes Associated with Seizure Freedom

Approximately 86–87% of surgical patients became seizure free long term.

Seizure freedom was associated with:

• greater educational attainment

• reduced disability

• increased independent living

• improved quality of life

Employment outcomes were less clear because many participants were still in education at follow-up.

This demonstrates that epilepsy surgery affects far more than seizures alone. Cognitive and psychosocial development are strongly influenced by successful seizure control.

IQ Change Across the Post-Operative Period

One of the most important findings was that cognitive recovery is extremely gradual.

IQ improvements were often not statistically significant until more than 6 years after surgery.

This is clinically important because standard hospital follow-up often occurs only:

• 1 year

• 18 months
  after surgery.

However, early assessments predict only around 25% of long-term IQ outcome.

This means short-term follow-up substantially underestimates long-term developmental recovery.

Effect of Medication Withdrawal

Children who successfully discontinued anti-seizure medication (ASM/AED withdrawal) often showed major cognitive improvement.

Medication withdrawal was associated with approximately a 10-point cognitive boost in some children.

This is important because anti-epileptic medications can impair:

• processing speed

• attention

• alertness

• learning efficiency

Once medications are withdrawn, children may show rapid improvements in these domains.

Large Longitudinal Surgery Cohorts

A later study combined data across multiple cohorts:

• n = 100

• 3–7 neuropsychological assessments per child

The developmental trajectory showed:

1. Decline before surgery

2. Stabilisation after surgery

3. Gradual upward recovery afterwards

This pattern strongly supports the idea that uncontrolled epilepsy progressively disrupts development, while successful surgery may reverse some of this developmental slowing.

Eriksson et al. (2024): Large GOSH Cohort

This study analysed approximately 500 children treated between 2000–2018.

Key Findings

Seizure freedom improved long-term intellectual trajectories

Children who became seizure free showed upward developmental trends over time.

Children who continued having seizures showed flatter or declining trajectories.

Medication withdrawal also improved outcome

Children who were seizure free and off medication showed the strongest improvements.

These findings reinforce the idea that both seizure control and reduction of medication burden contribute to cognitive recovery.

Structural Brain Plasticity After Surgery

A major question is whether post-surgical cognitive recovery reflects real brain changes.

Studies measuring grey matter volume found strong correlations between:

• increases in grey matter volume
  and

• increases in IQ

Findings

Study 1

R² = 0.31

Study 2

R² = 0.37

This means approximately one-third of the variance in IQ change could be explained by structural brain changes.

Why This Finding Is Important

Children lose brain tissue during surgery, particularly temporal lobe tissue.

Despite this, some children later show:

• increases in grey matter volume

• cognitive recovery

• improved intellectual functioning

This suggests the developing brain can reorganise after successful surgery.

The findings provide evidence for structural neuroplasticity rather than simple psychometric artefacts.

Post-Surgical Memory Changes

A major concern after temporal lobe surgery is memory decline because surgery may remove:

• hippocampus

• temporal neocortex

• temporal pole

These regions are essential for episodic and semantic memory.

Gleissner et al. (2005): Short-Term Memory Recovery

This study compared adults and children after temporal lobe surgery using verbal learning tasks.

Findings

Children

• showed an initial drop after surgery

• recovered substantially by 12 months

Adults

• showed persistent deficits

• demonstrated less recovery

Children therefore show greater functional recovery than adults after temporal lobe surgery.

This provides strong evidence for developmental plasticity.

Prentice et al.: Memory Change 12–18 Months After Surgery

This study examined delayed word-pair recall and delayed story recall.

Findings

Most children remained stable

The majority showed no major decline in memory.

Some children declined

Declines were most common after:

• left mesial temporal resections

• hippocampal resections

Some children improved

Particularly at the type of memory mainly handled by the side of the brain that was not operated on.

Factors Predicting Post-Surgical Memory Change

Three major predictors moderated memory outcome:

1. Pre-operative memory ability

2. Age at surgery

3. Hippocampal resection

Pre-Operative Memory Ability

Children with higher pre-operative memory scores were more likely to decline after surgery.

This likely reflects the fact that:

• intact hippocampal systems are still functioning well before surgery

• removing those structures causes greater detectable loss

Children with already impaired memory may show less measurable decline because memory systems were already disrupted.

Age at Surgery

Children operated on after approximately 12 years of age were more likely to show memory decline.

Younger children appear better able to compensate for loss of hippocampal tissue due to greater neuroplasticity.

This supports the idea that earlier intervention may sometimes improve developmental recovery.

Hippocampal Resection

The degree of hippocampal removal strongly influenced episodic memory outcome.

Children whose hippocampus was spared showed better memory preservation.

This finding has major surgical implications because surgeons increasingly attempt to preserve as much hippocampal tissue as possible.

Importantly, preserving hippocampal tissue does not appear to reduce seizure freedom rates.

Long-Term Memory Outcome (≈9 Years Post-Op)

Long-term follow-up demonstrated substantial recovery and reorganisation.

Left ATL Surgery

Children may initially show declines in verbal episodic memory, but many partially recover over time.

They also often show gains in visual memory.

Right ATL Surgery

Children often show gains in verbal memory over time.

Visual memory tends to stabilise.

This suggests that the “healthy” hemisphere can compensate for some lost functions through long-term plasticity.

Material Specificity After Surgery

The findings support material specificity models of temporal lobe memory organisation.

Left Temporal Surgery

Associated with:

• verbal episodic memory decline

• semantic memory difficulties

Right Temporal Surgery

Associated more with:

• visual/non-verbal memory systems

However, compensatory improvements often occur in contralateral memory systems.

Extent of Resection and Memory Outcome

Researchers carefully measured how much tissue was removed after surgery.

This revealed important structure-function relationships.

Temporal Pole and Semantic Memory

Semantic memory outcomes correlated strongly with integrity of the temporal pole. (The temporal pole is the very front tip (“pole”) of the temporal lobe).

Measures associated with temporal pole preservation included:

• receptive vocabulary

• category fluency

Children with extensive temporal pole resections often showed stagnation of vocabulary development, particularly around adolescence.

This strongly supports the role of the anterior temporal lobe as a semantic memory hub.

Hippocampal Volume and Episodic Memory

Preserved hippocampal volume correlated with:

• story recall

• verbal episodic memory

• delayed recall performance

This reinforces the central role of the hippocampus in episodic memory.

Voxel-Based Lesion Symptom Mapping (VLSM)

Voxel-based lesion symptom mapping linked post-operative IQ decline to temporal neocortical damage.

Particularly affected were:

• verbal comprehension

• semantic processing

These findings further support distributed-plus-hub models of semantic memory.

Contralateral Memory Improvements

One of the most striking findings was improvement in memory functions associated with the non-operated hemisphere.

Examples:

• after left surgery → visual memory gains. After seizures stop, the right hemisphere may start functioning better and more efficiently.

• after right surgery → verbal memory gains. Once seizures are controlled: the left hemisphere may work more effectively.

Possible explanations include:

• release from epileptic disruption

• improved network efficiency

• neuroplastic reorganisation

• improved educational participation after seizure freedom

Before surgery, seizures and abnormal electrical activity constantly interfere with brain networks.

Even the healthy hemisphere can be “distracted” or disrupted by this abnormal activity.

After surgery:

• seizure activity decreases

• the healthy side is no longer constantly disrupted

So it is “released” from interference and can work better.

Think of it like removing background noise so someone can finally concentrate properly.

Structural Plasticity and Cognitive Gains

Post-operative MRI studies demonstrated:

• increased grey matter volume

• contralateral brain changes

• frontal lobe changes

• hippocampal volume increases

These changes correlated with:

• IQ recovery

• episodic memory recovery

This suggests recovery is biologically meaningful rather than purely behavioural.

Long-Term Developmental Trajectories

Long-term outcomes fell into three broad groups:

Children who became seizure free and discontinued medication had the best outcomes.

Why Long-Term Follow-Up Is Essential

Short-term follow-up misses many important changes because:

• recovery is slow

• development continues over many years

• cognitive gains accumulate gradually

• different cognitive domains recover at different speeds

Processing speed often improves first after medication withdrawal.

Language and crystallised abilities recover much more slowly because they depend on ongoing learning and environmental exposure.

Early vs Late Surgery

Early-Onset Severe Epilepsy

For very early severe epilepsy:

• earlier surgery is generally better

• even radical surgery may improve long-term development

Later-Onset Focal Epilepsy

In focal epilepsy beginning later in childhood:

• some developmental scaffolding may already need to be established

• timing becomes more complex

Clinicians therefore balance:

• seizure control

• developmental timing

• educational demands

• surgical risks

Overall Conclusions

• Successful epilepsy surgery can significantly improve long-term developmental outcomes.

• Seizure freedom is one of the strongest predictors of cognitive recovery.

• Withdrawal of anti-epileptic medication contributes substantially to improvement.

• Cognitive recovery may continue for many years after surgery.

• Children demonstrate much greater neuroplasticity than adults.

• Episodic memory depends strongly on hippocampal integrity.

• Semantic memory depends strongly on temporal pole integrity.

• Larger resections increase risk of memory decline.

• Contralateral memory systems can improve after surgery.

• Structural brain plasticity is associated with cognitive recovery.

• Long-term follow-up is essential because early post-operative assessments underestimate recovery.

• Successful surgery may allow children to rejoin healthier developmental trajectories rather than continuing to fall behind peers.

Which temporal lobe structure is strongly associated with semantic memory?
The anterior temporal lobe/temporal pole.

What is hippocampal sclerosis (HS)?
Atrophy and scarring of the hippocampus associated with epilepsy and memory impairment.

What is a DNET?
A dysembryoplastic neuroepithelial tumour; a benign developmental tumour commonly causing epilepsy.

Why do children with DNETs often have better episodic memory than children with HS?
Because the hippocampus is often structurally intact.

What type of memory impairment is most associated with hippocampal sclerosis?
Episodic memory impairment.

What type of memory impairment is associated with left anterior temporal lesions?
Semantic memory impairment.

What did developmental amnesia demonstrate about the hippocampus?
That the hippocampus is critical for episodic memory.

How is semantic memory relatively preserved in developmental amnesia?
Because semantic knowledge is distributed across cortical networks.

What does “material specificity” mean in TLE?
Different hemispheres specialise in different memory types.

Which hemisphere is more associated with verbal memory?
Left hemisphere.

Which hemisphere is more associated with visual/non-verbal memory?
Right hemisphere.

What is lesion-negative TLE?
Epilepsy with no obvious structural lesion visible on MRI.

Why is lesion-negative TLE important?
Patients can still show widespread network abnormalities despite a “normal” MRI.

What is the main goal of epilepsy surgery?
Seizure freedom.

Why can epilepsy surgery improve cognition?
Because reducing seizures allows more normal brain development and functioning.

What factors contribute to cognitive impairment in TLE besides seizures?
Sleep disruption, medication side effects, missed schooling, and social disruption.

Why is early-onset epilepsy especially harmful?
Because it disrupts brain development during critical developmental periods.

What cognitive pattern is often seen before surgery in TLE?
Progressive lag behind normal developmental trajectories.

What happened to IQ trajectories after successful surgery?
Many children stabilised or improved developmentally.

What percentage of children showed developmental catch-up after surgery?
Approximately 26%.

What is developmental catch-up?
Developing faster than expected after successful seizure treatment.

What is neuroplasticity?
The brain’s ability to reorganise and adapt after injury or surgery.

Why do children recover better after temporal lobe surgery than adults?
Children have greater neuroplasticity.

What was one major finding about long-term recovery after surgery?
Improvements may continue for more than 6 years post-operatively.

Why are short-term follow-ups insufficient after epilepsy surgery?
Because cognitive recovery is very gradual and may take years.

How does anti-epileptic medication affect cognition?
It can reduce processing speed, attention, and alertness.

What cognitive ability often improves quickly after medication withdrawal?
Processing speed.

What is the relationship between hippocampal volume and episodic memory outcome?
Greater preserved hippocampal volume predicts better episodic memory.

What is the relationship between temporal pole integrity and semantic memory?
Greater preserved temporal pole tissue predicts better semantic memory.

What happened after left temporal surgery in some children?
Visual memory improved.

What happened after right temporal surgery in some children?
Verbal memory improved.

Why can contralateral memory systems improve after surgery?
Because seizures no longer disrupt the healthy hemisphere and networks reorganise.

What did voxel-based morphometry studies show in TLE?
Widespread grey matter abnormalities beyond the hippocampus.

What did diffusion imaging studies show in TLE?
Widespread white matter abnormalities and network disruption.

What does seizure freedom strongly predict after surgery?
Better cognitive and developmental outcome.

Why does preserving hippocampal tissue matter surgically?
Because it reduces risk of episodic memory decline.

Why does preserving temporal pole tissue matter surgically?
Because it helps preserve semantic memory and vocabulary development.

What is the major developmental concept in paediatric epilepsy surgery?
Successful treatment can change developmental trajectories rather than simply stop decline.

• Temporal lobe epilepsy (TLE) is a common focal epilepsy often resistant to medication and frequently treated surgically.

• Major causes include hippocampal sclerosis (HS), DNET tumours, cortical dysplasia, and other developmental abnormalities.

• The hippocampus is critical for episodic memory; the anterior temporal lobe/temporal pole is important for semantic memory.

• Episodic memory = autobiographical events tied to time/place; semantic memory = general knowledge and concepts.

• Left temporal lobe is more associated with verbal memory; right temporal lobe with visual/non-verbal memory.

• Developmental amnesia showed severe episodic memory impairment despite relatively preserved semantic memory, proving hippocampal importance for episodic memory.

• Semantic dementia supports the idea that the anterior temporal lobe acts as a semantic memory hub.

• Children with hippocampal sclerosis show major episodic memory impairment regardless of lesion side.

• Children with DNETs often show relatively preserved episodic memory because the hippocampus is intact.

• Left anterior temporal lesions are associated with poorer semantic memory.

• Memory deficits in paediatric TLE are less strongly lateralised than in adults because children’s brains are still developing.

• TLE affects distributed brain networks, not just focal lesions.

• Grey matter and white matter abnormalities extend beyond the temporal lobe.

• Lesion-negative TLE means no visible MRI lesion despite epilepsy; widespread network abnormalities may still exist.

• Chronic epilepsy can progressively disrupt developmental trajectories and widen the gap from healthy peers over time.

• Early seizure onset is strongly associated with poorer intellectual outcome because seizures disrupt critical periods of brain development.

• Additional contributors to cognitive impairment include sleep disruption, medication side effects, missed schooling, and social disruption.

• Epilepsy surgery aims to achieve seizure freedom while minimising cognitive harm.

• Successful surgery can improve IQ, educational attainment, independence, and quality of life.

• Seizure freedom and withdrawal of anti-epileptic medication are major predictors of cognitive recovery.

• Cognitive recovery after surgery is slow and may continue for more than 6 years.

• Short-term post-operative assessments underestimate long-term outcome.

• Children show much greater recovery after temporal lobe surgery than adults because of neuroplasticity.

• Some children show developmental catch-up after surgery, meaning they develop faster than expected afterwards.

• Episodic memory outcome depends strongly on preserved hippocampal tissue.

• Semantic memory outcome depends strongly on preserved temporal pole tissue.

• Larger resections increase risk of cognitive decline, especially verbal and semantic memory decline after left-sided surgery.

• Contralateral memory systems may improve after surgery (e.g. right hemisphere visual memory after left surgery).

• Structural brain plasticity occurs after surgery, including increases in grey matter volume associated with IQ gains.

• Processing speed often improves quickly after medication withdrawal; language-based skills recover more slowly.

• Successful surgery can allow children to rejoin healthier developmental trajectories rather than continuing to fall behind peers.