C. Apathy and loss of initiative or its opposite, slight elevation of mood, increased talkativeness, tendency to joke inappropriately (witzelsucht), lack of tact, difficulty in adaptation
D. If entirely prefrontal, no hemiplegia; but grasp and suck reflexes or instinctive grasping may be released
E. Anosmia with involvement of orbital parts
II. Effects of right frontal disease
A. Left hemiplegia
B. Changes as in I.B, C, and D
III. Effects of left frontal disease
A. Right hemiplegia
B. Broca aphasia with agraphia, with or without apraxia of the lips and tongue (see Chap. 22)
C. Sympathetic apraxia of left hand (see “Apraxia” in Chap. 3)
D. Changes as in I.B, C, and D
IV. Effects of bifrontal disease
A. Bilateral hemiparesis
B. Spastic bulbar (pseudobulbar) palsy
C. If prefrontal, abulia or akinetic mutism, lack of ability to sustain attention and solve complex problems, rigidity of thinking, bland affect, social ineptitude, behavioral disinhibition, inability to anticipate, labile mood, and varying combinations of grasping, sucking, obligate imitative movements, utilization behavior
D. Decomposition of gait and sphincter incontinence
The sylvian fissure separates the superior surface of each temporal lobe from the frontal lobe and anterior parts of the parietal lobe. There is no natural anatomic boundary between the temporal lobe and the occipital or the parietal lobe but the angular gyrus serves as a landmark for the latter. Figure 21-1 indicates the boundaries of the temporal lobes. The inferior branch of the middle cerebral artery supplies blood to the convexity of the temporal lobe, and the temporal branch of the posterior cerebral artery supplies the medial and inferior aspects, including the hippocampus.
The temporal lobe includes the superior, middle, and inferior temporal, lateral occipitotemporal, fusiform, lingual, parahippocampal, and hippocampal convolutions and the transverse gyri of Heschl. The last of these constitutes the primary auditory receptive area and is located within the sylvian fissure. It has a tonotopic arrangement: fibers carrying high tones terminate in the medial portion of the gyrus and those carrying low tones, in the lateral and more rostral portions (Merzenich and Brugge). The planum temporale (area 22), an integral part of the auditory cortex, lies immediately posterior to the Heschl convolutions, on the superior surface of the temporal lobe. The left planum is larger in right-handed individuals. There are rich reciprocal connections between the medial geniculate bodies and the Heschl gyri. These gyri project to the unimodal association cortex of the superior temporal gyrus, which, in turn, projects to the paralimbic and limbic regions of the temporal lobe and to temporal and frontal heteromodal association cortices and the inferior parietal lobe. There is also a system of fibers that project back to the medial geniculate body and to lower auditory centers. The cortical receptive zone for labyrinthine impulses is less well demarcated than the one for hearing but is probably situated on the inferior bank of the sylvian fissure, just posterior to the auditory area. Least well delimited is the role of the medial parts of the temporal lobe in olfaction and gustatory perception, although seizure foci in the region of the uncus (uncinate seizure) often excite hallucinations of these senses.