PET activation studies comparing two speech tasks widely used in surgical mapping

Area of Science:

• Neuroscience
• Cognitive Science
• Speech Pathology

Background:

• Automatic speech, such as counting, is often spared in aphasia, making it valuable for language mapping.
• The neural underpinnings of automatic speech, particularly counting, remain incompletely understood.
• Comparing automatic speech with word production tasks can elucidate distinct neural substrates.

Purpose of the Study:

• To compare the neural activity associated with automatic speech (counting) and word production (naming animals) in healthy and aphasic subjects.
• To investigate the brain regions involved in these tasks using functional brain imaging.
• To understand the differences in neural processing between propositional and automatic speech.

Main Methods:

• Behavioral and functional brain imaging (PET rCBF) data were collected from normal and aphasic participants.
• Tasks included counting, naming animals, non-verbal vocalizations, and quiet rest.
• Partial least squares analysis was used to analyze functional imaging data.

Main Results:

• In healthy subjects, naming and vocalizing activated bilateral anterior areas; naming alone engaged frontal and temporal regions; counting (automatic speech) showed a trend towards right and subcortical activation.
• In aphasic patients, naming and vocalization identified various cerebral sites, but no distinct neural variable for counting emerged.
• Behavioral data showed differences between groups in naming but not in counting or vocalizations.

Conclusions:

• Word generation tasks are more likely to engage classical language areas than automatic speech tasks like counting.
• Distinct neurological substrates may underlie non-propositional and automatic speech.
• Further research is needed to fully differentiate the neural basis of automatic and propositional speech.