Higher Order Cognition: Language

Language as a Higher Order Cognitive Function

• Often equated to speech, but it encompasses more than just speech.
• It is a computational cognitive capacity arising from functionally separable internal and external components.
• Involves speech perception, production, comprehension, repetition, reading, and writing.
• Aphasia: The inability to produce and/or comprehend speech fluently despite intact hearing and motor function (Friederici, Chomsky, Brevick et al., 2017).

Language Evolution

• Human communication differs from that of other species.
• Non-human primates use vocalization in different contexts.
• Motor control and gestures play a role in language evolution (Pollick & de Wall, 2007).
• Human auditory language evolved from competence in comprehension of sounds and gestures already existing in primate ancestors.

Language Lateralisation

• Language is largely lateralized in terms of its neural mechanisms.
• The left hemisphere is dominant for speech and language function in up to 90% of cases.
• This includes production and comprehension.
• The right hemisphere also plays a role, e.g., in non-verbal and emotion comprehension, spatial relations, prosody, and rhythm.
• Left hemisphere activation is seen in a verb generation task (adapted from Carlson, 2020).

Bilingualism/Multilingualism

• The ability to speak two or more languages.
• Inquires whether the underlying mechanisms are the same or different across languages.
• Reviews of studies with patients suggest there are common and language-specific regions (Guissani et al., 2007).

Language Production: Origins

• The ability to produce meaningful language.
• Paul Broca made the first link between language production and brain function.
• This was based on a patient, Leborgne, with a massive lesion in the left inferior frontal cortex.
• The patient was also named Tan, because he could only produce this syllable.

Language Production: Deficits

• Broca’s Aphasia
  • Also called non-fluent aphasia or expressive aphasia.
  • Patients cannot speak fluently, often skip grammatical/function words, and often get stuck while articulating.
  • The ability to grasp the meaning of spoken words is not affected, while speech production is impaired.
  • Assessed by spontaneous speech, picture description, or repetition tasks (e.g., Boston Diagnostic Aphasia Examination: The ‘Cookie Theft’ Description Task).

Language Production: Neural Correlates

• The inferior prefrontal cortex plays a key role.
• Lesions are mostly very deep and reach the basal ganglia, in particular, the head of the caudate nucleus.
• fMRI evidence shows tasks that activate Broca's area include phonological monitoring, rhyming tasks, repetition, stem completion, grammatical and syntactic tasks, and semantic tasks (to some degree).
• Lesion studies and fMRI evidence point to the same region in the inferior frontal gyrus.
• Involves Broca’s Area (IFG), Premotor Cortex, and Motor Cortex.

Language Comprehension: Origins

• The ability to understand language.
• Carl Wernicke made the first link between language comprehension and brain function.
• This was based on patient studies with lesions in certain brain areas.

Language Comprehension: Deficits

• Wernicke's Aphasia
  • Also called fluent aphasia or receptive aphasia.
  • Patients cannot understand spoken language very well and often produce meaningless language.
  • The ability to grasp the meaning of spoken words is impaired, while speech production is not affected.
  • Assessed by word recognition tasks and following commands tasks (e.g., The Token Test).

Language Comprehension: Neural Correlates

• The posterior superior temporal cortex plays a key role.
• Neuropsychological lesion and fMRI studies are complementary and point to the same area.
• The area is mainly activated by sentence/word comprehension tasks.

Language: Production vs. Comprehension

• Double Dissociation
  • Broca's and Wernicke’s aphasias constitute a double dissociation, demonstrating that there are separate systems in the brain that underpin either language comprehension or language production.
  • However, pure cases of these neuropsychological conditions are extremely rare.

Language Comprehension: Semantic Dementia

• On the one hand, it is a memory deficit linked to semantic memory; on the other hand, it is a language comprehension deficit.
• Inquires about comprehension deficits when Wernicke’s area is intact, relating to tissue loss and metabolic dysfunction.

Language Comprehension: Semantic Dementia

• Speech elicits greater activation compared to environmental sounds in the left superior temporal cortex (which includes Wernicke's area).
• The superior temporal cortex is more active when the brain processes auditory verbal information than when it processes nonverbal information.

The Hub & Spoke Model of Semantic Processing

• Reference to Ralph, Jefferies, Patterson, Rogers (2017): The neural and computational bases of semantic cognition.

Language Comprehension: Neural Correlates Revised

• Striate Cortex + Visual Association Cortex = written input
• Planum Temporale + Wernicke’s Area = spoken input
• Supramodal Semantic Hub.

Language: Repetition

• Simply the ability to repeat a sound, syllable, word, phrase, stanza, or a whole pattern.
• Very important for language learning.
• We can repeat words even without understanding them.
• Ultimately, repetition should lead to comprehension.

Language Repetition: Deficits

• Conduction Aphasia
  • Also called associative aphasia.
  • Patients can understand and produce language fairly well but are unable to repeat non-words (made-up words with no meaning).
  • Assessed with repetition tasks.

Language Repetition: Neural Correlates

• The arcuate fasciculus plays a role.
• It is a major white matter tract buried in the inferior parietal lobe.
• It connects Broca's and Wernicke’s areas.
• Damage leads to conduction aphasia.

Part 1 Summary

• Language processing is widely distributed throughout the brain.
• It is linked to primary auditory processing and the function in the transverse (Heschl’s) gyrus.
• Inferior prefrontal regions (including Broca’s area): motor programming of speech and speech production, syntax, and semantics.
• Superior temporal regions (including Wernicke’s area): auditory language perception, phonological processing & comprehension.
• Meaning processing involves a distributed network of unimodal sensorimotor cortices PLUS a supramodal hub region in the anterior temporal lobe.
• The arcuate Fasciculus facilitates language repetition.