**3. Auditory imagery**

330 Neuroimaging for Clinicians – Combining Research and Practice

brain anatomy, which increases sensitivity while maintaining selectivity. In comparison to Positron Emission Tomography (PET), fMRI offers increased statistical power for two reasons: first, the activation maps from multiple individuals do not need to be averaged, and the spatial transformation is not necessary, providing an enormous advantage in terms of signal-to-noise ratios (Watson et al., 1993); second, scanning can easily be extended over

Because of these advantages, fMRI has been used extensively to identify brain structures uniquely involved in cognitive functions, included mental imagery. This accordingly makes fMRI more suitable than PET and Single Photon Emission Computer Tomography (SPECT) for examining the extent to which imagery and perception share overlapping cortical areas in the functioning of various sensory modalities. In exploring this issue, researchers aimed to clarify whether imagery involves the activation of primary sensory cortices in visual, auditory, tactile, olfactory, gustatory, motor, and proprioceptive modalities. The present review is therefore aimed at investigating the status of fMRI research in all imagery modalities, with separate sections for each imagery modality, followed by collective

Visual imagery relies on the "mind's eye" and has traditionally been associated with the visual buffer (Kosslyn, 1980) or the visuo-spatial sketchpad of working memory (Baddeley & Loogie, 1992). In particular, Kosslyn (1980, 1994) proposed that visual imagery of a known object is generated from a semantic representation that accesses stored visual information about the object. This visual information is then loaded into a short-term "visual buffer", which functions as a coordinate space that temporarily maintains and manipulates information. Though some constraints are present, research has found that visual mental images can be rotated (Shepard & Metzler, 1971), scaled (Larsen & Bundesen, 1978), scanned (Kosslyn et al., 1978), transformed in shape and color (Dixon & Just, 1978), and inspected

Although these studies appeared to lead to the conclusion that visual imagery and visual perception share common mechanisms and processes, fMRI was used to clarify that the recruitment of the primary visual cortex (calcarine fissure - BA 17) may vary according to different factors. In a previous review Kosslyn & Thompson (2003) suggested that this contradiction in the literature may be accounted for by the fact that the primary visual cortex can be activated when the sensitivity of the neuroimaging technique is high (e.g., using fMRI rather than PET), and when inspecting details of visual mental images with high resolution to visualize shapes rather than spatial patterns. Amedi et al. (2005) later demonstrated that deactivating the auditory cortex, as measured by BOLD functional magnetic resonance imaging, may differentiate between visual imagery and visual perception. During visual imagery, the deactivation of the auditory cortex is negatively correlated with the activation of the visual cortex as well as with scores on the subjective Vividness of Visual Imagery Questionnaire (VVIQ) (Marks, 1973). When using fMRI, however, primary visual cortex activity correlated with the reported vividness of visual images when participants were instructed to visualize themselves or another person either bench pressing or stair climbing (Cui et al., 2007), or imagining concrete objects (e.g., to see a

time.

conclusions.

**2. Visual iImagery** 

(Thompson et al., 2008).

bucket) (Olivetti et al., 2009).

Intons-Peterson (1992, p. 46) defined auditory imagery as "the introspective persistence of an auditory experience, including one constructed from components drawn from long-term memory, in the absence of direct sensory instigation of that experience''. This type of imagery runs auditory traces from prior experiences (e.g., someone's voice, environmental sounds, melodies) through the "mind's ear". In this section, the fMRI studies on auditory verbal imagery will be presented first, followed by auditory imagery of environmental sounds, and musical imagery will be discussed last.

#### **3.1 Auditory verbal imagery**

Auditory verbal imagery can occur spontaneously or deliberately when recalling the sound of our own voice or someone else's voice. Within the frame of working memory, auditory verbal imagery has been associated with the operation of the phonological loop sub-system (Baddeley & Loogie, 1992). Two components have been discerned: a short-lived store that represents material in phonological form (inner ear), and an articulatory rehearsal process (inner voice) that is used to recode and refresh decaying representations into the phonological store (Smith et al., 1995).

By using fMRI, Shergill et al. (2001) found that there is a lack of activation in the primary auditory cortex (Heschel gyrus – BA 41/42) during auditory verbal imagery. Relative to the baseline condition (listening to each word carefully), first person imagery (imagining sentences of the form "I like…" in ones' own voice) showed no activation in the auditory cortex, while second and third person imagery (imagining sentences of the form "You like…." and "He likes…." in voices that participants had heard on a tape) showed activation in the secondary auditory cortex (BA 22), namely in the superior temporal gyrus. Jancke &

How fMRI Technology Contributes to the Advancement of Research in Mental Imagery: A Review 333

condition) yielded activations in the bilateral Heschl's gyrus, superior temporal gyrus, and left fusiform gyrus, and planum temporale. In contrast, the imagery condition consisted of watching the same movies presented in the perception condition but without the appropriate sounds, which had to be imagined by the participants. This condition elicited bilateral hemodynamic responses only in the right superior temporal gyrus, including the

Musical imagery is a type of auditory imagery that relies upon the capacity to mentally conceptualize songs, tunes, and general musical input. Musical imagery processes the tempo, temporal extension (Halpern, 1988), pitch (loudness) (Intons-Peterson Russell & Dressel, 1992), and timbre (sound quality of different instruments or voices) of real music (Pitt & Crowder, 1992). The first event-related fMRI study showed activation in the bilateral primary and secondary auditory areas in the superior temporal gyri when participants imagined a single computer-generated note (Yoo et al., 2001). The results also revealed significant activation in the medial and inferior frontal gyri, precuneus, middle frontal gyri, superior temporal gyri, and anterior cingulate gyri. This suggests that fMRI may be sensitive at least to the activation caused by simple internally generated sounds. This study, however, had no control conditions or task validation, and did not isolate timbre. Halpern et al. (2004) examined musical imagery of timbre relative to the visual imagery control. They found that the former activated the posterior temporal cortex, but not the primary auditory cortex, whereas the perception condition (judgments of the timbres of sounds) activated

No activation was found in the primary auditory cortex during musical imagery, even in musicians. Langheim et al. (2002) asked to musicians to imagine musical performances for 30 seconds alternated with resting periods. Relative to the resting condition, musical imagery activated supplementary motor and pre-motor areas, right superior parietal lobule, right inferior frontal gyrus, bilateral mid-frontal gyri, and bilateral lateral cerebellum. Yet, Lotze et al. (2003) did not find any activation of the primary auditory cortex when asking amateurs and professional violinists to mentally perform Mozart's "Violin concerto in G major" (KV216). During the musical imagery condition, professionals recruited the supplementary motor area, the superior premotor cortex, anterior areas (Larsell's lobule HVI) in the left cerebellar hemisphere, and bilateral superior parietal areas. Latter Zatorre et al. (2010) carried out two fMRI experiments with musicians. Participants were presented with the first few notes of a familiar tune (Experiment 1) or its title (Experiment 2), followed by a string of notes that was either an exact or an inexact reversal. The task was to judge whether the second string was correct or not by mentally reversing all its notes, which required both maintenance and manipulation of the represented string. During the reversal process, neither experiment showed activation of the primary auditory cortex, but both showed activation of the superior parietal lobe (intraparietal sulcus). Ventrolateral and dorsolateral frontal cortices were also activated, consistent with the memory load required during the task. Authors interpreted these results in the context of other mental transformation tasks, such as mental rotation in the visual domain, which are known to

Kraemer et al. (2005) conducted the only fMRI study that showed activation in the primary auditory cortex. In this study, participants were asked to listen to excerpts of songs with

primary and secondary auditory areas with some right-sided asymmetry.

bilateral planum temporale.

recruit the intraparietal sulcus region.

**3.3 Musical imagery** 

Shah (2004) also showed that the primary auditory cortex was not activated during auditory verbal imagery. Relative to the resting condition, imagining hearing a syllable (e.g., Ka, Ta, Pa) yielded activation in the bilateral superior temporal gyri, including the planum temporale, and the dorsal bank of the superior temporal sulcus. By exploring the fMRI correlates of auditory verbal imagery associated with the phonological processing of words, Aleman et al. (2005) confirmed the lack of activation of the primary auditory cortex. Participants were presented with bi-syllabic words and were required to indicate the syllable that carried the stress, discriminating between weak-initial words and strong-initial words. In the perceptual condition, words were delivered by headphones, whereas in the imagery condition, words were presented on a screen and participants were instructed to imagine hearing the word being spoken by another person. Results revealed that both perceptual and imagery conditions activated the bilateral supplementary motor area, bilateral post-central gyrus, bilateral insula, the left inferior frontal gyrus (Broca's area), the posterior left superior temporal sulcus/superior temporal gyrus, and the left intra-parietal sulcus/superior parietal lobule. Kim et al. (2008) reported a deactivation in the left superior temporal cortex (BA 22/42) and anterior cingulated cortex during auditory verbal imagery of another's remarks expressed toward self, which were derogatory in content, relative to auditory verbal imagery of another's remarks expressed toward self, which were nonderogatory and neutral in content. In addition, activation was found in both medial frontal cortex, left inferior frontal cortex, both pre-central gyrus, both inferior parietal lobule, right occipital-temporal cortex, left occipital cortex, both posterior insula, and both amigdala.

#### **3.2 Auditory imagery of environmental sounds**

This type of auditory imagery can occur spontaneously or deliberately when recalling the sound produced by environmental objects or auditory sources, such as the ringing of the phone, the shot of a gun, or sound produced by animals. In this direction, Olivetti Belardinelli et al. (2004a) investigated the neural correlates of mental imagery in different sensory modalities, including the auditory modality, by contrasting imagery sentences (e.g., hearing a shot) with abstract sentences (e.g., the power of reason). Relative to the abstract condition, there was no activation found in the primary auditory cortex during auditory imagery. There was, however, activity in the left middle temporal gyrus (BA 22/37), left inferior temporal gyrus (BA 37), left inferior-middle frontal gyrus, left inferior parietal lobule, and left insula. Using the same methodology, Olivetti Belardinelli et al. (2009) found a bilateral activation in the Heschl's gyrus comparing high-vivid participants with low-vivid participants in generating auditory images of environmental sounds, and in the right hemisphere of the same gyrus regressing the vividness scores of auditory images onto the bold signal. These activations, however, were not significant at the corrected threshold for multiple comparisons. Significant activations were found in the left middle frontal gyrus, right angular gyrus, right posterior cingulate, and left lingual gyrus. Authors explained the lack of significant modality-specific activation in the Heschl's gyrus in the light of the interference of the scanner noise on the auditory image formation process, which may have led to signal decrease solely in the primary auditory cortex, as showed by Gaab et al. (2007). Nonetheless, Bunzeck et al. (2005) used the fMRI technique and did not find any activation of the primary auditory cortex during imagery of familiar complex environmental sounds, either. Compared to watching a silent scrambled movie of familiar scenes (control condition), watching familiar scenes and listening to the corresponding sounds (perception condition) yielded activations in the bilateral Heschl's gyrus, superior temporal gyrus, and left fusiform gyrus, and planum temporale. In contrast, the imagery condition consisted of watching the same movies presented in the perception condition but without the appropriate sounds, which had to be imagined by the participants. This condition elicited bilateral hemodynamic responses only in the right superior temporal gyrus, including the bilateral planum temporale.
