The connectional anatomy of visual mental imagery: evidence from a patient with left occipito-temporal damage

Abstract

Most of us can use our “mind’s eye” to mentally visualize things that are not in our direct line of sight, an ability known as visual mental imagery. Extensive left temporal damage can impair patients’ visual mental imagery experience, but the critical locus of lesion is unknown. Our recent meta-analysis of 27 fMRI studies of visual mental imagery highlighted a well-delimited region in the left lateral midfusiform gyrus, which was consistently activated during visual mental imagery, and which we called the Fusiform Imagery Node (FIN). Here, we describe the connectional anatomy of FIN in neurotypical participants and in RDS, a right-handed patient with an extensive occipito-temporal stroke in the left hemisphere. The stroke provoked right homonymous hemianopia, alexia without agraphia, and color anomia. Despite these deficits, RDS had normal subjective experience of visual mental imagery and reasonably preserved behavioral performance on tests of visual mental imagery of object shape, object color, letters, faces, and spatial relationships. We found that the FIN was spared by the lesion. We then assessed the connectional anatomy of the FIN in the MNI space and in the patient’s native space, by visualizing the fibers of the inferior longitudinal fasciculus (ILF) and of the arcuate fasciculus (AF) passing through the FIN. In both spaces, the ILF connected the FIN with the anterior temporal lobe, and the AF linked it with frontal regions. Our evidence is consistent with the hypothesis that the FIN is a node of a brain network dedicated to voluntary visual mental imagery. The FIN could act as a bridge between visual information and semantic knowledge processed in the anterior temporal lobe and in the language circuits.

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Brain Structure and Function
https://doi.org/10.1007/s00429-022-02505-x
ORIGINAL ARTICLE
The connectional anatomy ofvisual mental imagery: evidence
fromapatient withleft occipito‑temporal damage
DouniaHajhajate1· BrigitteC.Kaufmann1· JianghaoLiu1,2· KatarzynaSiuda‑Krzywicka1· PaoloBartolomeo1
Received: 15 February 2022 / Accepted: 29 April 2022
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2022
Abstract
Most of us can use our “mind’s eye” to mentally visualize things that are not in our direct line of sight, an ability known as visual
mental imagery. Extensive left temporal damage can impair patients’ visual mental imagery experience, but the critical locus of
lesion is unknown. Our recent meta-analysis of 27 fMRI studies of visual mental imagery highlighted a well-delimited region
in the left lateral midfusiform gyrus, which was consistently activated during visual mental imagery, and which we called the
Fusiform Imagery Node (FIN). Here, we describe the connectional anatomy of FIN in neurotypical participants and in RDS, a
right-handed patient with an extensive occipito-temporal stroke in the left hemisphere. The stroke provoked right homonymous
hemianopia, alexia without agraphia, and color anomia. Despite these deficits, RDS had normal subjective experience of visual
mental imagery and reasonably preserved behavioral performance on tests of visual mental imagery of object shape, object color,
letters, faces, and spatial relationships. We found that the FIN was spared by the lesion. We then assessed the connectional anatomy
of the FIN in the MNI space and in the patient’s native space, by visualizing the fibers of the inferior longitudinal fasciculus (ILF)
and of the arcuate fasciculus (AF) passing through the FIN. In both spaces, the ILF connected the FIN with the anterior temporal
lobe, and the AF linked it with frontal regions. Our evidence is consistent with the hypothesis that the FIN is a node of a brain
network dedicated to voluntary visual mental imagery. The FIN could act as a bridge between visual information and semantic
knowledge processed in the anterior temporal lobe and in the language circuits.
Keywords Perception and imagery· Patients· Cerebrovascular· Behavioral· Lesion mapping· White matter tractography·
Stroke
Introduction
Visual mental imagery denotes our ability to use our “mind’s
eye” to mentally visualize things that are not in our direct line
of sight. Brain-damaged patients with extensive left temporal
damage often have impaired visual mental imagery (Barto-
lomeo 2002, 2008; Bartolomeo etal. 2020; Spagna 2022),
but the crucial lesion site in the temporal cortex is unknown.
Our recent meta-analysis of 27 fMRI studies of visual men-
tal imagery (Spagna etal. 2021) highlighted the importance
of a well-delimited region within the FG4 field (Lorenz etal.
2015) of the left midfusiform gyrus, that we labeled Fusiform
Imagery Node (FIN). This finding is consistent with the avail-
able neuroanatomical evidence from lesion neuropsychology,
neuroimaging, and direct cortical stimulation, which indicates
the left inferior temporal lobe as the region most commonly
implicated in voluntarily generated mental images (Liu etal.
2021). The localization of the FIN in the left ventral temporal
cortex suggests a possible role as a bridge between domain-
preferring visual regions (Mahon and Caramazza 2011) and
amodal semantic networks (Fairhall and Caramazza 2013;
Lambon Ralph etal. 2017), perhaps including the language
circuits (Bouhali etal. 2014).
However, neuroimaging evidence such as that coming
from the Spagna etal.’s (2021) meta-analysis is correlative,
not causal. To establish a causal role of FIN in visual men-
tal imagery, the study of brain-damaged patients is manda-
tory. Here, we describe patient RDS, a 58-year-old, right-
handed patient who 7years before testing had an extensive
Dounia Hajhajate and Brigitte Kaufmann shared first position.
* Paolo Bartolomeo
paolo.bartolomeo@icm-institute.org
1 Sorbonne Université, Institut du Cerveau-Paris Brain
Institute-ICM, Inserm, CNRS, AP-HP, Hôpital de La Pitié-
Salpêtrière, 75013Paris, France
2 Dassault Systèmes, Paris, Vélizy-Villacoublay, France

Brain Structure and Function
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left occipito-temporal stroke. The stroke provoked right
homonymous hemianopia, alexia without agraphia, and
color anomia. These deficits and their neuroanatomical cor-
relates were extensively described in previous papers (Siuda-
Krzywicka etal. 2019, 2020), and were stable at the time of
the present testing. Despite his deficits, RDS had preserved
mental imagery introspection and behavioral performance.
To estimate the importance of FIN for visual mental imagery
in this patient, we mapped it on the native space of his brain.
Moreover, we assessed its connectional anatomy by mapping
it and the lesion in the MNI and native spaces; we then visu-
alized the fibers of the two most important long-range white
matter tracts passing through the FIN, the inferior longitu-
dinal fasciculus (ILF), and the arcuate fasciculus (AF). We
chose to examine these two major pathways because of their
likely role in linking the FIN to the processing of semantic
information in the anterior temporal lobe (Lambon Ralph
etal. 2017) and in the perisylvian language network (Bouhali
etal. 2014).
Methods
We used a French version (Santarpia etal. 2008) of the VVIQ
questionnaire (Marks 1973) to assess RDS’s subjective viv-
idness of visual mental imagery. In Santarpia etal.’s (2008)
classification based on neurotypical controls, scores ≤ 46 indi-
cate low imagery vividness, scores 47–65 indicate average viv-
idness, and scores ≥ 66 indicate high vividness. In addition,
the patient and a group of 18 neurotypical participants, aged
22–48, performed a computerized version of the BIP—Battérie
Imagerie-Perception (Bourlon etal. 2009). The current ver-
sion of the battery assesses imagery of object shapes (Fig.1A),
object colors (Fig.1B), faces (Fig.1C), letters (Fig.1D), and
spatial relationships on an imaginary map of France (Fig.1E)
(Bartolomeo etal. 2005; Bourlon etal. 2008, 2011). On each
trial, participants hear a pair of nouns followed by an adjective:
e.g., “cherries… strawberries… dark”. They are requested to
vividly imagine the items they hear. Immediately after, par-
ticipants have to select the noun that is best represented by
the adjective: in the previous example, it is “cherries”, which
are darker than strawberries. Then, they go on to indicate the
overall vividness of their mental images on a 4-level Likert
Fig. 1 Examples of trials of the visual mental imagery battery per-
formed by patient RDS. In different trials, participants are invited
to decide about A the overall shape of animals or objects (round or
long); B which fruit or vegetable is darker or lighter in color; C the
general facial shape of celebrities (round or oval); D which handwrit-
ten word contains at least one ascender (t, l, d), or a descender (j, p,
y); E which of 2 auditorily presented cities is left or right of Paris
in an imaginary map of France. The perceptual task F is similar to
the imagery tasks, except that stimuli are presented in an audio-visual
format

Brain Structure and Function
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scale, pressing one of 4 buttons, where button 1 represents
“no image at all” and button 4 represents a “vivid and realistic
image”. RDS performed a slightly more extended version of
the battery (18–20 items per imagery domain) than controls
did (12 items per domain). A perceptual control task (Fig.3F)
employed the same stimuli used for the imagery tasks, except
that stimuli were presented in an audio-visual format.
To compare RDS’s performance with controls’, we used
SingleBayes_ES.exe, a tool for Bayesian analysis of asingle
case using a case–control design (Crawford and Garthwaite
2007). The program uses Bayesian Monte Carlo methods to
test whether an individual’s score is significantly below the
scores of controls, such that the null hypothesis that it is an
observation from the control population can be rejected, and
provides a point estimate of the abnormality of the scores.
Here, two-sided p values were considered as statistically sig-
nificant at p < 0.05, and credible intervals are reported.
To assess the spatial relationships of the FIN with the
patient’s lesion, we took the FIN volume from our meta-anal-
ysis (Spagna etal. 2021) and co-registered it to the patient’s
T1 images in the native space.
To identify the fibers that are connected to the FIN, we
usedthe functional ROI derived from our meta-analysis
(Spagna etal. 2021). We visualized the fibers of two major
white matter tracts passing through the FIN volume: the occip-
ito-temporal ILF (Catani etal. 2003), and the AF (Catani etal.
2005). Fiber tracking was done on the group average template
constructed from a total of 1065 subjects (Fig.3A), that comes
with DSIstudio (https:// dsi- studio. labso lver. org/). A multishell
diffusion scheme was used, and the b-values were 990,1985
and 2980s/mm2. The number of diffusion sampling directions
were 90, 90, and 90, respectively. The in-plane resolution was
1.25mm. The slice thickness was 1.25mm. The diffusion
weighted images were resampled at 2.0mm isotropic. The
b-table was checked by an automatic quality control routine
to ensure its accuracy (Schilling etal. 2019). The diffusion
data were reconstructed in the MNI space using q-space dif-
feomorphic reconstruction (Yeh and Tseng 2011) to obtain
the spin distribution function (Yeh etal. 2010). A diffusion
sampling length ratio of 1.7 was used. The output resolution
of is 2mm isotropic. The restricted diffusion was quantified
using restricted diffusion imaging (Yeh etal. 2017). A deter-
ministic fiber tracking algorithm (Yeh etal. 2013) was used
with augmented tracking strategies (Yeh 2020) to improve
reproducibility.
To identify the fibers that are connected to the FIN, the
functional ROI derived from a meta-analysis including 27 arti-
cles was used (Spagna etal. 2021) (specification of FIN: MNI
coordinates -42, -54, 18). To grow this region into the white
matter, a dilatation by 1mm was applied in DSIstudio.
For fiber tracking, the anatomy prior of a tractogra-
phy atlas (Yeh et al. 2018) was used to separately map
“Inferior_Longitudinal_Fasciculus_L” and the “Arcuate_
Fasciculus_L” with a distance tolerance of 16mm. A seeding
region was placed at “Inferior_Longitudinal_Fasciculus_L”
and the FIN served as an ROI (Fig.3 in orange; Supplemen-
tary Video 1). The same procedure was also used to identify
fibers of the “Arcuate_Fasciculus_L” that are connected to
the FIN (Fig.3 in blue; Supplementary Video 1). The ani-
sotropy threshold, the angular threshold (between 15 to 90
degrees), and the step size (from 0.5 voxel to 1.5 voxels)
were randomly selected. Tracks with length shorter than
10mm or longer than 200mm were discarded. For visuali-
zation purposes, a total of 500 tracts were calculated. Topol-
ogy-informed pruning (Yeh etal. 2019) was applied to the
tractography with 16 iterations to remove false connections.
To visualize the spatial relationships of the brain lesion
with the FIN connections, the patient’s structural MRI image
was normalized into MNI space using the normalization tool
in the Brain voyager software (https:// www. brain voyag er.
com/). The patient’s brain lesion was then manually deline-
ated by an experienced rater, using the MRIcron software
(https:// www. nitrc. org/ proje cts/ mricr on/).
For fiber tracking in the patient’s native space (Fig.3B),
a DTI diffusion scheme was used, and a total of 60 diffusion
sampling directions were acquired. The b value was 1505s/
mm2. The in-plane resolution was 2mm. The slice thickness
was 2mm. The diffusion MRI data were rotated to align
with the AC-PC line. The tensor metrics were calculated
using DWI with b value lower than 1750s/mm2. For fiber
tracking, the same procedure explained above was used. To
match the patient’s anatomy, the functional ROI of the FIN
(Spagna etal. 2021) was co-registered to the patient’s indi-
vidual T1-weighted MRI using spm12 toolbox in Matlab.
The resulting neuroanatomical localization in the patient
space was checked and corrected by an experienced rater.
To identify the cortical areas that connected by the fibers
passing through the FIN, as well as the fibers that were dam-
aged by the lesion, we used the connectivity matrix function
in DSI studio. For the HCP1065 template, several matrices
representing the number of fibers terminating within regions
of the FreeSurferDKT_Cortical atlas (Desikan etal. 2006)
were calculated. The connectivity matrix was calculated
using the count of the connecting tracks restricted to the
left hemisphere. In creating the connectivity matrix, the
ROIs were specified as pass regions (Ghulam-Jelani etal.
2021). In total, four connectivity matrices were generated;
two fascicles (AF or ILF) passing through two ROIs (FIN
or Lesion).

Brain Structure and Function
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Results
RDS reported vivid visual mental imagery overall. His viv-
idness score was 77, close to the ceiling score of 80 of the
French version (Santarpia etal. 2008) of the VVIQ, and
higher than the 66 cutoff score that Santarpia etal. indi-
cated for high vividness. RDS is thus a high vividness
subject on the VVIQ. For each domain of the battery, the
mean trial-by-trial subjective vividness was 3.8/4 (object
shape) 2.7/4 (object color), 3.7/4 (letters), 3.1/4 (faces), and
3.5/4 (map of France). RDS’s performance on the battery
(Table1) revealed reasonably preserved abilities in all the
tested imagery domains. No significant difference emerged
between RDS’s performance and controls’, except for the
map of France, where he was 72% correct. This level of
performance was worse than controls’ (who were 75%-100%
correct), but better than the 50% chance level (binomial test,
p = 0.049).
On the perceptual control task, RDS’s performance was at
or near ceiling (range 95–100% correct).
T1-weighted MRI (Fig.2) showed that RDS’s ischemic
lesion encompassed the calcarine sulcus, the lingual, fusiform,
and parahippocampal gyri in the left hemisphere, as well as the
callosal splenium. In the fusiform gyrus, the lesion’s lateral
border corresponded to the midfusiform sulcus (see Fig.2).
Thus, the FG4 field, which lies lateral to the midfusiform sul-
cus (Lorenz etal. 2015) and contains the FIN (Spagna etal.
2021), was entirely spared by the lesion.
White matter tractography (Fig.3, Supplementary video)
demonstrated intact fibers passing through the FIN and belong-
ing to two main systems: the ILF, linking the FIN to occipital
regions and to anterior temporal regions important for semantic
knowledge (Lambon Ralph etal. 2017), and the AF, connecting
the FIN to perisylvian language circuits (Catani etal. 2005). Most
intact ILF fibers connected the regions labeled as left_fusiform
and left_inferior_temporal in the Desikan etal.’s atlas (Desikan
etal. 2006). Many ILF fibers leading to left_lateral_occipital,
Table 1 Performance (number and percentage of correct responses) of RDS and controls on the visual mental imagery battery
a Crawford and Howell (1998); the results are for a two-tailed test
b Crawford and Garthwaite (2002)
Task Control sample RDS’s score Significance
testaEstimated percentage of
the control population
obtaining a lower score
than RDSb
Estimated effect size (zcc)
nMean SD (%) t p Point (95% CI) Point (95% CI)
Object shape 18 10.18/12 (85%) 12.25 15/18 (83%) −0.159 .876 43.764% 26.50–61.96 −0.163 −0.625 to 0.304
Object color 18 9.19/12 (77%) 16.45 16/20 (80%) 0.178 .861 56.944% 38.74–74.09 0.182 −0.286 to 0.646
Letters 18 11.62/12 (97%) 5.16 19/20 (95%) −0.377 .711 35.540% 19.50–53.89 −0.388 −0.861 to 0.098
Faces 18 10.13/12 (83%) 9.07 14/20 (70%) −1.395 .181 9.052% 1.85–22.44 −1.433 −2.087 to −0.758
Map of France 18 10.87/12 (91%) 5.99 13/18 (72%) −3.087 .007 0.334% 0.00–2.22 −3.172 −4.315 to −2.011
Fig. 2 T1-weighted MRI showing RDS’s lesion (yellow) in native space, as well as the FIN location (orange)

Brain Structure and Function
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left_lingual, left_pericalcarine, and left_superior_temporal
were instead disconnected by the lesion. Concerning the AF,
most intact fibers connected left_inferior_temporal to left_pars_
opercularis, left_caudal_middle_frontal, and left_rostral_mid-
dle_frontal; fewer fibers connected left_inferior_temporal with
left_pars_triangularis and left_precentral. The lesion mainly
disconnected fibers going from left_inferior_temporal to
left_caudal_middle_frontal.
Fig. 3 Connectional anatomy of the FIN (red), and its spatial rela-
tionship with a reconstruction of the patient’s lesion (green). Fib-
ers passing through the FIN are visualized from two major tracts:
the ILF (orange), which connects the FIN to occipital and tempo-
ral areas, and the AF (blue). Panel A shows the fibertracking on the
HCP1065.2 mm template, Panel B shows the fibertracking on the
patient’s individual DTI, both with automated fiber tracking that
come with DSIstudio (Version 2021.12.03 by Yeh; http:// dsi- studio.
labso lver. org/). The Supplementary video https:// bit. ly/ 3JrFY se)
shows a 3D visualization of the ILF fibers and the AF fibers passing
through the FIN, and their spatial relationship with the patient’s brain
lesion

Brain Structure and Function
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Discussion
The occipito-temporal stroke suffered by RDS extensively
damaged the portion of the left fusiform gyrus situated medi-
ally to the midfusiform sulcus, but spared its lateral part,
which contains the FIN (Spagna etal. 2021) in cytoarchi-
tectonic sector FG4 (Lorenz etal. 2015). Lesion reconstruc-
tion and white matter tractography strongly suggest that the
connectivity of the FIN with the anterior temporal lobe and
with language circuits was also spared by the lesion. RDS’s
intact introspection and reasonably preserved performance
for visual mental imagery, together with the preservation
of the FIN, are thus consistent with the hypothesis of a
causal implication of the FIN in this ability. Moreover, in
this patient, the FIN could not communicate with the left
primary visual cortex, which was totally destroyed by the
lesion; as a consequence, our data support the additional
hypothesis that visual mental imagery engages the FIN in a
top–down fashion, perhaps through the ILF from the ante-
rior temporal lobe important for semantic processing (Lam-
bon Ralph etal. 2017), and through the AF from prefrontal
regions and language circuits. The present results thus add
to extensive neuropsychological evidence (Bartolomeo etal.
2020; Liu etal. 2021; Spagna 2022) against the dominant
model of visual mental imagery, which emphasizes the role
of primary visual cortex in this ability (Kosslyn etal. 1995,
1999; Pearson 2019). In principle, however, other spared
occipito-temporal regions could contribute to RDS’s visual
mental imagery. For example, primary visual cortex was
intact in the right hemisphere. However, it is of note that, in
the present patient, splenial disconnection (which was dem-
ostrated in a previous study using white matter tractography,
see Siuda-Krzywicka etal. 2019) prevented any direct com-
munication between the right, intact primary visual cortex
and the posterior part of the left hemisphere. Thus, putative
contributions of the right-hemisphere primary visual cortex
to FIN functioning should have traveled indirectly through
more anterior callosal connections.
Our conclusions are based on RDS’s performance 7 years
after his stroke. This extended time lapse could have allowed
plastic phenomena to occur. Against this possibility, we note
that RDS’s deficits in reading and color naming were stable
over the years. Moreover, testing at closer temporal intervals
from the stroke may suffer from another potential confounding
factor, the occurrence of diaschisis phenomena (Bartolomeo
2011). For example, in patients with severe strokes, gray matter
blood flow in the homolog regions of the opposite hemisphere
can be decreased for several months, and may approach nor-
mal levels only 12–24months post-stroke (Meyer etal. 1993).
Note, however, that even 7 years post-stroke RDS’s face
imagery scores were numerically inferior to those for other
domains. Face imagery may engage the right-hemisphere
fusiform face area (O'Craven and Kanwisher 2000), and thus
require inter-hemispheric integration. In RDS, perhaps inter-
hemispheric communication was still partially dysfunctional
at the time of testing, as a consequence of splenial disconnec-
tion. A similar point might be advanced for RDS’s impaired
performance on the test based on the map of France, which is
also likely to require inter-hemispheric integration (Rode etal.
2010). Further evidence from the follow-up of brain-damaged
patients, coupled with advanced neuroimaging, is needed to
discriminate between the sometimes contradictory roles of
the nondamaged hemisphere in post-stroke cognitive deficits
(Bartolomeo and Thiebaut de Schotten 2016).
The present evidence only indirectly speaks to the causal
role of the FIN in visual mental imagery. However, our results
nicely complement more direct evidence coming from brain-
damaged patients with impaired visual mental imagery. For
example, two patients found themselves unable to build visual
mental images after a closed head trauma (Moro etal. 2008).
In both cases, the damage affected the left BA 37, and was
likely to include the lateral portion of the fusiform gyrus with
the FIN. Traumatic brain injuries, like those suffered by Moro
etal.’s patients, typically provoke diffuse axonal injury, which
is likely to disrupt white matter connectivity in the large-scale
brain networks supporting visual mental imagery (Bartolomeo
2008; Mechelli etal. 2004). Thus, FIN dysfunction leading to
impaired visual mental imagery should not be interpreted in
a localist way, but as a source of perturbation of large-scale
brain networks (Bartolomeo 2011). Another patient with left
temporal damage had impaired perception and imagery for
orthographic material, but not for other domains (Bartolomeo
etal. 2002). Damage or disconnection of domain-preferring
regions such as the visual word form area (Dehaene and Cohen
2011) may account for such domain-selective deficits of visual
mental imagery, as opposed to domain-general imagery defi-
cits which, in the present framework, may instead result from
FIN dysfunction.
In apparent contradiction with the present evidence, a recent
case report (Thorudottir etal. 2020) described patient PL518,
an architect who spontaneously complained to have become
unable to visualize items after a bilateral stroke in the territory
of the posterior cerebral artery. The lesion included the left
medial fusiform gyrus, but spared its lateral portion. How-
ever, the lesion did extend more laterally in the fusiform white
matter than similar lesions in patients without visual mental
imagery deficits (see their Fig.3A). Thus, disconnections
within the fusiform white matter might have contributed to FIN
dysfunction and consequent visual mental imagery impairment
in PL518, perhaps in combination with the extensive accom-
panying lesions in the right hemisphere, which might have
deprived the left hemisphere of potential inter-hemispheric
compensation (Bartolomeo and Thiebaut de Schotten 2016).
Taken together with these previous studies, the present
evidence suggests a crucial role for the FIN in visual mental

Brain Structure and Function
1 3
imagery. Specifically, the FIN might integrate, on the one
side, elements of semantic knowledge stored in the anterior
temporal lobe (Lambon Ralph etal. 2017; Persichetti etal.
2021), and distributed linguistic representations (Popham etal.
2021), with, on the other side, high-level visual representations
in domain-preferring regions in the ventral temporal cortex
(Mahon and Caramazza 2011). Following the lead of Heinrich
Lissauer’s seminal ideas (Bartolomeo 2021; Lissauer 1890;
Lissauer and Jackson 1988), we propose that dissociations in
performance between perceptual and imagery abilities may
emerge when the FIN or other high-level visual regions in the
ventral temporal cortex are deafferented from perceptual input
processed in more posterior regions. Such posterior discon-
nections would result in impaired perception with preserved
imagery (Bartolomeo etal. 1998). The present evidence sug-
gests that, in these cases, visual mental imagery would be sup-
ported by the ILF and AF connections to the FIN.
A more direct test of this model would have required fMRI
evidence of spared FIN activity during visual mental imagery
in our patient; unfortunately, however, when we attempted such
an experiment RDS had a panic reaction in the MRI machine,
and subsequently declined to participate in any further neuro-
imaging exams. As a consequence, the localization of the FIN
in the patient’s brain must be considered as a (likely) approxi-
mation, because it derives from our meta-analysis of fMRI
studies (Spagna etal. 2021). Finally, we note that although
single patient studies can achieve a level of detail unattain-
able in group studies, without extensive replication, one cannot
always exclude the influence of idiosyncratic variations of the
mind/brain (Bartolomeo etal. 2017). This seems, however,
unlikely for RDS, because there are reasons to consider his
premorbid neurocognitive profile as representative of the gen-
eral population (Siuda-Krzywicka etal. 2019). Accumulating
evidence from in-depth studies of other patients, with brain
lesions inducing or not deficits of visual mental imagery, will
be important to confirm or refute the present model.
Author contributions All authors contributed to the study conception and
design. Material preparation and data collection were performed by DH,
JL, and KSK. Analyses were performed by BK, DH, and JL. The first
draft of the manuscript was written by PB and all authors commented on
previous versions of the manuscript. All authors read and approved the
final manuscript.
Funding This work was supported by Agence Nationale de la Recherche
through ANR-16-CE37-0005 and ANR-10-IAIHU-06 to PB, by the École
des Neurosciences Paris Île de France to KSK, and bySwiss National
Science Foundation Grant No.P2BEP3_195283to BK.
Data availability Data will be made available on reasonable request.
Declarations
Conflict of interest The authors declare they have no relevant financial or
non-financial interests to disclose.
Ethical approval All subjects gave written consent according to the Dec-
laration of Helsinki. The study was promoted by the Inserm (C13-41) and
approved by the Ile-de-France I IRB committee.
Consent to participate Informed consent was obtained from all individual
participants included in the study.
Consent to publish Consent to publish has been received from all par-
ticipants.
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