Anatomical Evidence of Multimodal Integration in Primate Striate Cortex

“Multisensory input into auditory cortex has been the focus of several studies (Falchier et al., 2002; Foxe et al., 2002; Rockland and Ojima, 2003; Murray et al., 2005; Cappe and Barone, 2005; Lakatos et al., 2007; Cappe et al., 2009) yet most of the recent attention regarding somatosensory and…”

“, 2003; Schroeder & Foxe, 2002); their laminar profile is consistent with the existence of both top-down (Falchier et al., 2002; Rockland & Ojima, 2003; Schroeder & Foxe, 2002; Schroeder et al., 2003) and bottom-up (Schroeder & Foxe, 2002; Schroeder et al.”

“This projection (Falchier et al. 2002; Rockland and Ojima 2003) is reported to originate from caudal auditory areas, as well as adjacent polysensory cortex, and to target primarily the peripheral representation of V1.”

“, 2011) and anatomical tracer studies in animals (Falchier et al., 2002), it is perhaps more plausible that this pathway is critically involved in other forms of multisensory processing.”

“It is possible that the cross-modal activation reflects genuine interactions between the different modalities and their neural substrates [Calvert et al., 1997; Falchier et al., 2002; Shimojo and Shams, 2001; Wallace et al., 2004].”

“Audiovisual interactionshavealso been implicated through direct anatomical connections between auditory and primary visual cortical areas (Falchier et al., 2002; Rockland and Ojima, 2003; Smiley and Falchier, 2009) and within higher-level multisensory processing areas such as the posterior parietal…”

“The first pathway consists of a direct, feedforward projections from primary or associative auditory/somatosensory cortices to early visual areas (Falchier et al., 2002; Rockland and Ojima, 2003; Cappe and Barone, 2005; Schroeder and Foxe, 2005; Cappe et al., 2009).”

“Injections in the far eccentricities of V1 reveal important connections with the core, belt and parabelt areas, opening further the possibility of mild multimodal integration in primary sensory areas (Falchier et al. 2002).”

“…auditoryareas byvisual processing has been reported in fMRI studies of bimodal attention (Johnson and Zatorre, 2005, 2006), and anatomical connections exist between auditory and visual areas that may mediate interactions between these modalities (Eckert et al., 2008; Falchier et al., 2002).”

“Sensitive anatomical studies revealed sparse auditory projections to visual cortices (Falchier et al., 2002; Rockland and Ojima, 2003; Budinger et al., 2006; Hall and Lomber, 2008).”

“Moreover, auditory and visual cortices are interconnected (Falchier et al., 2002; Rockland and Ojima, 2003; Bizley et al., 2007) and further connected to the medial temporal lobe (Witter and Groenewegen, 1986; Insausti et al.”

“Although evidence for this view has been growing rapidly in cortex (Falchier et al., 2002; Rockland and Ojima, 2003; Ghazanfar et al., 2005; Kayser et al., 2005; Lakatos et al., 2007; Lakatos et al., 2008; Kayser et al., 2010), ours is the first study to our knowledge that extends the prevalence of these modulatory ef…”

“Previous studies in animals proved the existence of projections from auditory cortical areas to visual cortical areas (Falchier et al., 2002; Rockland and Ojima, 2003).”

“LP receives input from SC and influences V1, and it has been shown to reduce background noise to enhance visual responses (Fang et al., 2020).”

“2009 for a review): anatomical connections between unisensory areas of different modalities have been observed (Falchier et al., 2002; Cappe and Barone 2005; Falchier et al. 2011).”

“These cross modal interactions within sensory-specific regions may be mediated by feedback connections from higher-level multisensory regions or by direct connections between regions that are normally considered to be unisensory (Altmann et al., 2007; Falchier et al., 2002; Noesselt et al., 2007).”

“Multisensory integration also appears to be a prominent feature of the caudal belt association areas, which have somatosensory and visual reponses and connections (Falchier et al., 2002; Rockland & Ojima, 2003; Schroeder et al., 2003; Kayser et al., 2007).”

“the existence of projections from the auditory to the visual cortex and multisensory feedback connections to primary visual areas (Falchier et al., 2002; Rockland and Ojima, 2003).”

“However, previous studies have found intracortical connections between the early sensory cortices suggesting a multimodal interplay (Falchier et al., 2002; Cappe and Barone, 2005; Budinger et al., 2006; Campi et al., 2010; Zingg et al., 2014; Henschke et al., 2015).”

“areas (Cappe and Barone, 2005; Clavagnier et al., 2004; Falchier et al., 2002; Rockland and Ojima, 2003; Sieben et al., 2013).”

“Far-peripheral visual areas also show distinct anatomical (Clavagnier et al., 2004; Falchier et al., 2002) and functional (Eckert et al., 2008) connectivity with auditory cortex (also shown in Fig.”

“Although many data in the literature support the existence of cross-modal links between the auditory and visual areas (Driver & Noesselt, 2008; Falchier, Clavagnier, Barone, & Kennedy, 2002; Ghazanfar & Schroeder, 2006; Rockland & Ojima, 2003; Schroeder & Foxe, 2005), it is quite difficult to infer…”

“…in the normal brain or after sensory input deprivation (Bizley and King, 2009; Finney et al., 2001; Lomber et al., 2010; Petrus et al., 2014; Wallace et al., 2004) and may be mediated by specific corticocortical projections (Budinger et al., 2006; Campi et al., 2010; Falchier et al., 2002).”

“Along these lines, recent anatomical studies have provided evidence for direct projections from the auditory cortex to the visual cortex in monkeys (Clavagnier, Falchier, & Kennedy, 2004; Rockland & Ojima, 2003; Falchier, Clavagnier, Barone, & Kennedy, 2002 ).”

“This functional organization by eccentricity is predicted by primate anatomical connectivity, 3,4 where cortical feedback projections from auditory and other non-visual areas preferentially target the periphery of early visual areas.”

“Auditory cortical signals project to V1 regions for the peripheral, but not central, visual field (Falchier et al., 2002), likely influencing the saliency map in V1.”

“Direct heteromodal corticocortical connections onto V1 have already been reported in macaque (Falchier et al. 2002; Rockland and Ojima 2003; Clavagnier et al. 2004; Borra and Rockland 2011), cat (Innocenti et al. 1988; Sanchez-Vives et al. 2006; Hall and Lomber 2008), mice (Larsen et al. 2009), and…”

“…have mostly reported direct reciprocal projections between visual areas V1/V2 and parabelt/caudal auditory regions in hearing monkeys and marmosets (Falchier et al. 2002, 2010; Rockland and Ojima 2003; Cappe and Barone 2005), which have been related to early audiovisual interactions (Cappe et al.…”

“Such findings are consistent with direct connections mediating early-latency, low-level multisensory interactions within visual cortices.”

“In primates and cats, auditory activation of the visual cortex upon binocular deprivation is limited to the cortical peripheral visual field representation (recently reviewed in [77]), in line with auditory afferent input exclusively targeting the peripheral visual field representation (primates: [79]; cats: [80]).”

“These interactions could be mediated by direct cortico-cortical connections between early auditory and visual cortices, which neuroanatomical studies in non-human primates have found to terminate predominantly in areas that represent the peripheral visual field [52, 53].”

“Moreover, direct anatomical connections between the superior temporal (auditory processing) and occipital regions (visual processing) in animals [55] and humans [56] have been confirmed that may play an important role in audiovisual integration.”

“This projection is weak on the part of area V1 that represents the central visual field, but it is far from being negligible when considering the representation of the peripheral visual field, where it has been shown to be as strong as the projection from the visual areas of the superior temporal sulcus (Falchier et a…”

“…where the subscript t denotes the t th cycle, are projected to the thalamic subnetwork, mimicking the large number of neural projections from different cortical areas to the higher-order thalamus [41], [42] where G denotes the 1x1 convolutional layer to compress channels of features concatenated.”

“Anatomical evidence for early multisensory interactions comes from animal studies showing direct cross-connections between the visual and auditory cortex (Falchier et al. 2002; Smiley et al. 2007).”

“This hypothesis is consistent with the existence of projections from the polysensory areas of the temporal lobe to V1 in monkeys (Falchier et al., 2002), with the evidence that the primary visual cortex of rats responds to tactile discrimination of novel objects, and its activity correlates with…”

“Voss and colleagues [34] suggest that recruitment of visual cortex by auditory stimulation may be achieved through awakening of dormant horizontal connections between these cortices; such projections have recently been demonstrated in normal adult primates [10].”

“…sensory cortical domains typically characterized as unisensory (Morrell, 1972; Giard and Peronnet, 1999; Foxe et al., 2000; Schroeder et al., 2001; Falchier et al., 2002; Molholm et al., 2002; Schroeder and Foxe, 2002; Fu et al., 2003; Rockland and Ojima, 2003; Besle et al., 2004; Brosch et al.,…”

“Alternatively, the effects may be due to feedforward connections carrying information following the convergence between auditory and visual pathways at an early stage, including primary sensory cortices (Rockland & Van Hoesen, 1994; Falchier et al., 2002; Clavagnier et al., 2004; Smiley & Falchier, 2009).”

“Similarly, previous studies have suggested that the extent of multisensory processing and connectivity of low-level visual areas is modulated by their topographic organization (Borra and Rockland, 2011; Falchier et al., 2002; Gleiss and Kayser, 2013; Rockland and Ojima, 2003).”

“From tract tracing studies, there is also evidence of a direct connection between primary auditory and primary visual cortices in Macaca fascicularis monkeys [24].”

“…showed that integration can also occur at very early stages of cortical processing in regions that were traditionally considered to be unisensory (Foxe et al., 2000; Falchier et al., 2002, 2010; Molholm et al., 2002; Foxe and Schroeder, 2005; Smiley and Falchier, 2009; Molholm and Foxe, 2010).”

“The perceptual mechanism, for greater audiovisual integration in the periphery, may arise because of the larger number of neural projections from auditory cortex to visual cortex in the periphery (Falchier et al., 2002; Rockland & Ojima, 2003).”

“Anatomically, these effects could be mediated by direct axonal projections from auditory cortex to visual cortex or thalamocortical connections (Falchier et al. 2002; Campi et al. 2010; van den Brink et al. 2013).”

“In our opinion, the connections between auditory and visual cortex make it possible to alter the brain activity in the occipital areas [27, 81–86].”

“However, research evidence has accumulated over the last decade, which indicates that sensory processing may be more multisensory than initially believed, with previously assumed ‘unisensory’ areas displaying multisensory characteristics [2,4–8].”

“…human and animal studies, it is clear that a broad network of cortical (sensory and association areas—Barth et al., 1995; Schroeder et al., 2001; Falchier et al., 2002; Brett-Green et al., 2003) and subcortical (superior colliculus—Meredith and Stein, 1986; Wallace et al., 1993, 1998; Peck,…”

“It is in the extrinsic pathways that we were able to show that weights spanned a considerable distance, over 5 units of log, and that the weights were highly consistent across individuals (Falchier et al., 2002; Vezoli et al., 2004; Markov et al., 2011b).”

“For auditory–visual information, early sensory integration is grounded on multisensory neurons in the superior colliculus (Wallace and Stein 1997) along with direct (Falchier et al. 2002; Budinger and Scheich 2009; Cappe et al. 2009) and indirect (van den Brink et al.”

“, 2011b) and non-human primates (Falchier et al., 2002; Rockland and Ojima, 2003).”

“There are direct feedback connections from primary auditory and multisensory areas to V1 and V2 in macaque (Clavagnier et al., 2004; Falchier et al., 2002; Rockland and Ojima, 2003) and similar connections in rodents (Allman et al., 2008; Budinger et al., 2006).”

“Indeed, multisensory associative cortices and frontal regions downstream along sensory processing pathways project only, or more strongly, to central V1 [29,30].”

“…with previous studies reporting the existence of reciprocal projections between the VC and AC ( Bizley et al., 2007 ; Budinger et al., 2006 ; Falchier et al., 2002 ; Falchier et al., 2010 ; Rockland and Ojima, 2003 ), and provides a possible anatomical basis for the visual inputs of…”

“There is also neuroanatomical evidence that there are more projections from the primary auditory cortex to peripheral V1, in contrast to the very sparse projections to foveal V1 (Falchier et al., 2002).”

“Visual brain areas may always be involved in auditory information processing due to the anatomical and functional connections between the visual and auditory networks (Burton et al., 2012; Falchier et al., 2002; Gougoux et al., 2005; Shimony et al., 2006).”