Temporal Lobe

Temporal Lobe

Temporal Lobe Bryan Kolb, University of Lethbridge, Lethbridge, AB, Canada Ó 2015 Elsevier Ltd. All rights reserved. This article is a revision of the...

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Temporal Lobe Bryan Kolb, University of Lethbridge, Lethbridge, AB, Canada Ó 2015 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by K. Tanaka, volume 23, pp. 15595–15599, Ó 2001, Elsevier Ltd.

Abstract The temporal lobe is one of the four major divisions of the cerebral cortex. The function of the temporal lobe is to transform visual, auditory, and gustatory sensory input into higher-order perceptions and memory. Temporal lobe injury leads to a complex set of symptoms of both basic perceptual processes as well as higher-order processes such as memory and emotion.

Introduction The cerebral hemispheres can be grossly divided into four lobes (frontal, parietal, occipital, and temporal) that are largely defined by the cranial bone lying above them. The temporal lobes comprise all the tissue that lies below the lateral (Sylvian) fissure and anterior to the occipital lobe, including the limbic cortex on the medial surface of the temporal lobe (Figure 1). The temporal lobe also includes subcortical structures, including the amygdala and hippocampus and their associated cortical regions. This is a large volume of brain tissue that has multiple functions, including the processing of auditory, visual, and gustatory sensations, visuospatial information, aspects of emotion, and certain forms of memory.

Temporal Lobe Anatomy The human temporal regions can be divided on the lateral surface into those that are auditory (Brodmann’s areas 41, 42, and 22 in Figure 1(b)) and those that form the ventral visual stream on the lateral temporal lobe (areas 20, 21, 37, and 38 in Figure 1(b)). The visual regions are often referred to as inferotemporal cortex or by von Economo’s designation, TE. The temporal sulci enfold a lot of cortex. In particular, the lateral (Sylvian) fissure contains tissue forming the insula, which includes the gustatory cortex as well as the auditory cortex. The superior temporal sulcus (STS) separates the superior and middle temporal gyri and houses a significant amount of neocortex as well, as illustrated for the rhesus monkey in Figure 2, including many subregions of multimodal cortex that receive input from auditory, visual, and somatic regions as well as from prefrontal and posterior parietal regions. The medial temporal region includes the amygdala and adjacent cortex (uncus), the hippocampus and surrounding cortex (subiculum, entorhinal cortex, perirhinal cortex), and the fusiform gyrus (see Hippocampus and Related Structures). The cortical region lying along the boundary of the temporal and parietal lobes is often called the temporal–parietal junction (TPJ). This abstract label refers roughly to the region at the end of the Sylvian fissure, including the ventral regions of the angular and supramarginal gyri (see Parietal Lobe) and adjacent temporal cortex. The TPJ is consistently shown to be

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Figure 1 Gross anatomy of the temporal lobe. (a) Three major temporal lobe gyri are visible on its lateral surface. (b) Brodmann’s areas on the lateral surface, where auditory areas are shown in yellow and visual areas in purple. Areas 20, 21, 37, and 38, the inferotemporal cortex, are often referred to as TE. (c) The temporal lobe gyri visible in a medial view. The uncus is the anterior extension of the hippocampal formation. Reproduced from Kolb, B., Whishaw, I.Q., 2015. Fundamentals of Human Neuropsychology, seventh ed. Worth, New York.

International Encyclopedia of the Social & Behavioral Sciences, 2nd edition, Volume 24

http://dx.doi.org/10.1016/B978-0-08-097086-8.55051-X

Temporal Lobe

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Figure 2 Lateral view of the rhesus monkey brain with the Superior Temporal Sulcus opened up to reveal multiple subareas as identified by Seltzer, B., Pandya, D., 1978. Afferent connections and architectonics of the superior temporal sulcus and surrounding cortex in rhesus monkey. Brain Research 149, 1–24. Adapted from Kolb, B., Whishaw, I.Q., 2009. Fundamentals of Human Neuropsychology, third ed. Freeman, New York.

active in neuroimaging studies investigating attention, memory, language, and social processing. Thus, the TPJ is proposed as central to decision-making in a social context.

Functions of the Temporal Lobe We can identify five general functions of the temporal lobe: (1) processing of auditory input, (2) processing of visual input, (3) processing of gustatory input, (4) long-term storage of sensory input (memory), and (5) emotional regulation.

Processing of Auditory Input Sound waves reaching the ear stimulate a cascade of mechanical and neural events – in the cochlea, brainstem, and, eventually, the auditory cortex – that result in a percept of sound. The auditory cortex has multiple regions, each having a tonotopic map. The precise functions of these maps are poorly understood, but the ultimate goal is to perceive sound-making objects, locate sound, and make movements in relation to sound. Cells in the primary auditory cortex of mammals (Brodmann’s area 41, Figure 1) respond to distinct frequencies of sound, whereas cells in higher auditory cortical regions respond more to combinations of frequencies. In humans, there is another type of distinction as well. Specifically, two fundamental characteristics of sound are its frequency (spectral feature of sound) and timing (temporal feature). Thus, sounds vary in their frequencies as well as in how quickly they change. In a seminal paper, Zatorre and Belin (2001) demonstrated using positron emission tomography imaging that the primary auditory cortex in both hemispheres responds to temporal features and the higher areas responded to spectral features, but the higher auditory regions showed an asymmetry: the left was weighted toward temporal processing and the right toward spectral processing. There is considerable evidence that the analysis of speech

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requires rapid auditory processing (i.e., temporal features), whereas analysis of tonal information, such as music, requires the identification of changes in pitch (i.e., spectral features). Both speech and musical perception require more than just moment-to-moment analysis of temporal and spectral features, but there is also a memory component referred to as echoic memory. Echoic memory is crucial for auditory perception, because the meaning of any single sound depends upon the following sounds. Although the precise length of echoic memory is variable, it generally lasts about 3–4 s though some authors have shown it to last up to 20 s. Echoic memory appears to involve an extended network of cortical regions, but a key region is the superior temporal gyrus (e.g., Alain et al., 1998).

Processing of Visual Input The occipital lobe sends a major projection to multiple regions in the temporal cortex both in the middle and ventral temporal gyri (inferotemporal areas labeled TE in Figure 2), as well as the anterior tip of the superior temporal gyrus and the STS. The posterior parietal lobe sends connections to the medial temporal regions (hippocampus and parahippocampal regions). Neurons in the inferotemporal cortex are tuned for the features of objects and faces and many change their pattern of firing with experience, including how often a visual stimulus has been encountered and any association with reward. These properties make the ventral stream more tuned to the enduring characteristics of visual stimuli than with the moment-tomoment changes in the visual array, which provides a basis for object recognition. Another characteristic of inferotemporal neurons is that they provide a mechanism for the internal representation of images of objects. Fuster and Jervey (1982) first demonstrated that, if monkeys are shown specific objects that are to be remembered, neurons in the monkey cortex continue to discharge during the ‘memory’ period. These selective neuronal discharges may provide the basis of working memory for the visual stimuli (sometimes referred to as iconic memory). Furthermore, these discharges may provide the basis for visual imagery. That is, the discharge of groups of neurons selective for characteristics of particular objects may provide mental images of those objects in their absence. Regions of the ventral stream have surprisingly selective tuning to specific stimulus characteristics such as specific body parts (hands, bodies, faces), color, or scenes. One example is a region in the fusiform gyrus, the fusiform face area, which is selectively activated by faces (e.g., Kanwisher, 2010). Another is a more medial region in the hippocampal gyrus, the parahippocampal place area, which is preferentially active for scenes including buildings and places. This region is hypothesized to play a significant role in visuospatial navigation, reflected both in the specificity of activation to scenes as well as the input from the posterior parietal regions involved in directing movements in space (see Parietal Lobe; Cortical Areas Engaged in Movement: Neuroimaging Methods).

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A different type of visual analysis is performed by the STS. The STS receives multimodal inputs that play a role in categorizing stimuli. A major category is social perception, which includes analyzing actual or implied body movements (biological motion) that provide socially relevant information. This information plays an important role in social cognition, a ‘theory of mind’ that allows us to develop hypotheses about other people’s intentions. For example, the direction of a person’s gaze provides us considerable information about what that person is – or is not – attending to. Many cells in the STS are especially tuned to faces, including the precise orientation (e.g., head-on, profile) as well as specific facial expressions. Some cells in the STS are maximally sensitive to primate bodies moving in a particular direction, which is remarkable because the basic configuration of the stimulus is identical as the body moves in different directions; only the direction changes (see review by Barraclough and Perrett, 2011).

Processing of Gustatory Input The primary taste cortex is found in the insula (see Taste and Smell, Psychology of). The insula contains neurons tuned to the five basic tastes (sweet, salt, bitter, sour, and unami) as well as other neurons that encode oral somatosensory stimuli (viscosity, fat texture, temperature, and capsacin). Thus, our perception of taste is not just the basic tastes but also an interaction of the taste and texture of food. Human imaging studies using MRI have shown that insular activity correlates with the subjective intensity of tastes. The insula projects to the orbitofrontal cortex, which is likely the secondary taste area. Activation of the orbitofrontal cortex correlates with the subjective pleasantness of taste rather than the intensity (see Taste and Smell, Psychology of).

Memory Interest in the temporal lobes’ function in memory was stimulated in the early 1950s by the discovery that bilateral removal of the medial temporal lobes, including the hippocampus and amygdala, results in amnesia for all events after the surgery (anterograde amnesia). It is now clear that both the medial temporal regions play a central role in the extended neural circuitry underlying explicit memory. The key structures are the hippocampus, entorhinal cortex, perirhinal cortex, and parahippocampal cortex (Petri and Mishkin, 1994). Although it is not possible to distinguish the roles of these regions in humans, studies in monkeys are providing some insights. The perirhinal cortex appears to support memory for objects (including factual knowledge about the world), whereas of the hippocampus and parahippocampal regions, the hippocampal regions are central to the circuits underlying contextual knowledge (autobiographic, or episodic, knowledge). The amygdala also plays a role in memory, but is involved in a circuit underlying emotional memory. The amygdala has close connections with other medial temporal structures as well as the frontal lobe. It also sends projections to the brainstem structures that control autonomic responses such as blood pressure and heart rate, the hypothalamus that controls hormonal systems, and the periaqueductal gray matter that affects the perception of pain.

Emotional memory has been studied most thoroughly in fear conditioning (see Fear Conditioning: Overview). The amygdala seems to evoke our feelings of fear/anxiety toward stimuli that are threatening, but also can do the same toward stimuli that by themselves would not normally produce fear, such as is observed in anxiety disorders.

Emotional Regulation An interconnected network of structures including the neocortex, thalamus, hippocampal formation, and amygdala forms the basis of emotional experience (see Emotion, Neural Basis of). The amygdala receives input from all of the sensory systems. The amygdala can therefore create a complex image of the sensory world. To be excited, cells in the amygdala require complex stimuli such as faces. Thus, like the STS, the amygdala plays a role in identifying facial expressions. As noted earlier, the amygdala also interacts with brainstem structures that control autonomic responses and thus can link external stimuli with emotional feelings.

Symptoms of Temporal Lobe Injury Nine principal symptoms are associated with disease of the temporal lobes: (1) disturbance of auditory sensation and perception, (2) disorders of music perception, (3) disorders of visual perception, (4) disturbance in the selection of visual and auditory input, (5) impaired organization and categorization of sensory input, (6) inability to use contextual information, (7) impaired long-term memory, (8) altered personality and affective behavior, and (9) altered sexual behavior (Kolb and Whishaw, 2015). In contrast to damage in the primary visual or somatic regions, bilateral damage to the primary auditory cortex does not produce a complex loss of sensation (auditory deafness). Rather, damage to auditory cortex impairs the processing of speech sounds (left hemisphere) or in making pitch discriminations (right hemisphere). These deficits are consistent with the observation of aphasia in patients with large injuries of the left temporal regions including both the primary and secondary auditory regions, including Wernicke’s area. In contrast, damage to the superior temporal gyrus on the right disrupts the processing of musical sounds, the exact deficit depending upon the site of injury. For example, rhythm discrimination is most affected by right posterior superior temporal gyrus damage, whereas meter discrimination (for example, distinguishing a waltz and a march) is more affected by anterior damage to either temporal lobe. People with inferotemporal cortex injuries do not have field defects such as those with occipital lesions, but they do have deficits in the perception of complex scenes, reflecting the role of the inferotemporal cortex in the ventral stream of visual processing. Recall that neurons in TE show selective tuning to specific object characteristics so it is not surprising that temporal lesions would interfere with perceiving these characteristics and may produce specific visual agnosias. Persons with temporal lobe damage frequently report difficulties in attention to auditory or visual information when there are multiple competing inputs. For example, if two

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people are talking at once we usually can shift from listening to one and then the other. Temporal lobe patients have great difficulty in doing this and as a result get little from either speaker. Similarly, one strategy that we unconsciously use for understanding visual and auditory material is to categorize it. When asked to learn a list of words such as ‘dog, car, bus, apple, rat, lemon, cat, truck, orange,’ most of us will organize the words into three different categories – animals, vehicles, and fruit. If the list is later recalled, the items are likely to be recalled by category, and recall of the categories is likely to be used as an aid in recalling the items. Patients with temporal lobe injuries do not do this, leading to less efficient perception and memory of the information. Context plays an important role in normal perception and recall of sensory information. Seeing a familiar object or person in a novel context can often give us pause to identification. For example, encountering a clerk from your neighborhood store on a bus in Stockholm may provoke a feeling of familiarity but because the context is wrong, identification of the person is likely to be slow. It is clear that we use normally context as a cue in object identification. Patients with temporal lobe injuries are impaired at this ability, giving rise to both perceptual and memory difficulties. But memory deficits are larger than just those related to context. Temporal lobe injuries, especially those involving medial temporal lobe structures, can result in amnesia both for events preceding the injury (retrograde amnesia) as well as for events following the injury (anterograde amnesia) (see Amnesia: General; Declarative Memory, Neural Basis of). Finally, temporal lobe injury, especially when the amygdala is damaged, can produce profound changes in personality. Bilateral amygdala damage is associated with a loss of emotion, and especially fear. The general clinical impression is that temporal lobe patients have a clear personality change, sometimes referred to as a temporal lobe personality (e.g., Bear and Fedio, 1977). Symptoms include increased emotionality, depression, obsessionalism, religiosity, paranoia, and a reduced sense of humor.

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Conclusion In summary, the temporal lobe plays a central role in the higher-order analysis of auditory and visual information, and especially in context. As a result, temporal lobe injury leads to a complex set of symptoms of both basic perceptual processes as well as higher-order processes such as memory and emotion.

See also: Amnesia: General; Attention, Neural Basis of; Autobiographical Memory; Cortical Areas Engaged in Movement: Neuroimaging Methods; Declarative Memory, Neural Basis of; Emotion, Neural Basis of; Fear Conditioning: Overview; Hippocampus and Related Structures; Learning and Memory, Neural Basis of; Parietal Lobe; Spatial Navigation; Taste and Smell, Psychology of; Visual Streams: Dorsal and Ventral.

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