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).

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 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).

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).

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.

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).

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.

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.

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).

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.

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.

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.

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.

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

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.

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 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.