Transcortical Motor Aphasia:This language disorder is almost identical to Broca’s aphasia, in which a person cannot produce spontaneous speech. In essence, people with transcortical motor aphasia cannot say what they want to say. They simply can’t form the words. However, if you asked them to repeat something, they can do it without difficulty. For instance, a person with this disorder who wants to express that she is thirsty cannot say “I am thirsty." She could, however, repeat the sentence “I am thirsty” if she were asked to do so. Mild cases of transcortical motor aphasia can produce a form of hesitant speech known as telegraphic speech. This language disorder is typically caused by a stroke just in front of Broca’s area.
Transcortical Sensory Aphasia:People with this rare type of aphasia, cannot comprehend what others say to them, but they can speak fluently. Even though they can repeat words or sentences they hear others say, they cannot understand what those words or sentences mean. For instance, if you asked a person with transcortical sensory aphasia “Are you OK?” she might repeat a part of the question and say “you OK” or say “are you OK” in response. This type of aphasia is caused by injuries to brain areas which surround Wernicke’s language area, an area of the brain important in sensing and understanding language.
Mixed Transcortical Aphasia:People with this type of aphasia cannot speak or comprehend others when they speak, but they can repeat words or sentences, and sing songs that are familiar to them. In this rare type of aphasia, the main areas of language (Broca's and Werinicke's) are intact but their surrounding areas, also known as the language association areas, are damaged. It is thought that damage to these association areas leaves Broca's and Wernicke's areas completely isolated from the rest of the language system, thus precluding the production of spontaneous speech and the comprehension of spoken and written language. The most common cause of mixed transcortical aphasia is a watershed stroke of the language association areas as a result of severe internal carotid stenosis.
Sources: Bradley G Walter, Daroff B Robert, Fenichel M Gerald, Jancovic, Joseph Neurology in clinical practice, principles of diagnosis and management. Fourth Edition, Philadelphia Elsevier, 2004.
Bradley G Walter, Daroff B Robert, Fenichel M Gerald, Jancovic, Joseph Neurology in clinical practice, principles of diagnosis and management. Fourth Edition, Philadelphia Elsevier, 2004.Allan Ropper and Robert Brown, Adam's and Voctor's Principles of Neurology, 8th Edition McGraw-Hill Companies Inc., United States of America, 2005, pp 417-430.