Brain Maps and Beyond By Steven Vargas
History of Brain Mapping • Since the study of Phrenology, a now pseudoscience, people started to attribute certain brain areas with certain functions and behaviors. • Phineas Gage and his frontal lobe damage, which caused him major personality changes. • Wilder Penfield and his maps for sensory and motor corticies. • These and more findings have lead to popular theories of modularity .
Broca’s Aphasia • Discovered by French neurologist Paul Broca by looking at the brains of his patients after they died. • Located in left posterior inferior frontal gyrus or Broca’s area. • It is also know as expressive aphasia. • It is categorized by deficits in language production both spoken and written • Language comprehension is roughly intact.
Patient with Broca’s Aphasia • http://www.youtube.com/watch?v=gocIUW3E-go
Wernicke’s Aphasia • Discovered by Carl Wernicke around the same time Broca found Broca’s area. • Corresponds to damage to posterior part of the superior temporal lobe known as Wernicke’s area. • Categorized by fluent unintelligible speech and language comprehension deficits. • Also known as Receptive aphasia.
Lesion correlates of conversational speech production deficits • Goal was to tap into different aspects of speech production and distinguish potentially distinct neural mechanisms. • Prompted by fact that Brocas’s area was not as predictive of symptoms of expressive aphasia in past lesion studies. By Arielle Borovsky, Ayse Pinar Saygin, Elizabeth Bates, Nina Dronkers
Methods : Subjects • Used 50 aphasiacs with different types of a aphasias including Broca’s ,Wernicke’s, and anomic aphasia. • They had unilateral lesions caused by a cerebrovascular accident. • Recruited from the San Diego community and were paid fro participating in the study.
Methods: Variables • They interviewed the subjects asking them a list of interview questions which were recorded for fluent, complex and lexical speech. • “Tokens”: the overall number of words spoken which represents overall speech fluency. I.E. “Tall – parents – often – have – tall – kids” (tokens = 6, number of words: 6) • Mean length of utterance in morphemes(MLU):used to measure grammatical complexity. I.E. “Tall – parent – s(Plu) – often – have – tall – kid – s(Plu)” (MLU = 8, number of morphemes: 8 number of utterances: 1) • Type/Token Ratio(TTR): Number of different kinds of words spoken divided by overall number words spoken to measure lexical diversity. “Tall – parents – often – have – kids (TTR = 0.83, number of unique words: 5, number of words: 6)
Methods: Variables Cont. • They created digital reconstructions of their lesions using Voxel based lesion Symptom Mapping (VLSM). • VLSM: Technique in which at each voxel, patients are divided into two groups according to whether they did or did not have a lesion affecting that voxel. • These produce colored VLSM maps that represent voxels where patients with lesions show a significantly different production score than those whose lesions are spared that voxel.
Results • Speech fluency correlated with insula , motor cortex, and superior longitudinal fasciculus(SLF). • Complexity of speech correlated with anterior portion of insula, and motor cortex. • Lexical diversity corelated with anterior medial temporal gyrus(MTG)and superior temporal gyrus (STG).
Conclusions • They found that speech fluency and complexity overlap in lesion regions. • Deficits in production of fluent and complex speech were found in lesions in motor, somatosensory cortex, anterior insula and parts of SLF as well as IFG. • Posterior MTG, STG, Angular gyrus were involved in deficits in production of semantic variety in speech. • Changes the belief that these areas were only involved in comprehension of speech.
References Images • hiddentalents.org • images.wikia.com/psychology/images/0/0a/Sensory_and_motor_homunculi.jpg • http://www.nature.com/nrn/journal/v5/n10/fig_tab/nrn1521_F1.html • http://www.profelis.org/webpages-cn/lectures/neuroanatomy_1ns.html • http://4.bp.blogspot.com/_0N6mlRJGP78/R3MQ9HpuZcI/AAAAAAAAANw/xjCgh2d7FEc/s1600-h/Gray726.png • http://knakmos.deviantart.com/art/Perception-23682233 Facts • Wikipedia Article • Arielle Borovsky, Ayse Pinar Saygin, Elizabeth Bates, Nina Dronkers, 2007,Lesion correlates of conversational speech production deficits,Neuropsychologia volume 45, issue 11.